Method and apparatus for horticultural lighting with current sharing

ABSTRACT

A method and apparatus for a light fixture that uses current sharing across any one or more parallel LED strings within the light fixture. A processor determines the current requirements of the one or more LED strings that are needed to produce a given intensity level. The processor then apportions the current generation capability of a power supply across all active LED strings using time division multiple access (TDMA) whereby each LED string conducts its apportioned current within its allocated time slot to the mutual exclusion of the remaining active LED strings in any given time period. The light fixture utilizes LEDs with increased forward voltage interspersed with LEDs having reduced forward voltage in the same LED string. A processor utilizes shunt devices across the one or more LEDs with increased forward voltage to substantially match the cumulative forward voltage of each LED string.

FIELD OF THE INVENTION

The present invention generally relates to a horticultural lightingsystem, and more particularly to an adaptive horticultural lightingsystem for use indoors.

BACKGROUND

Light emitting diodes (LEDs) have been utilized since about the 1960s.However, for the first few decades of use, the relatively low lightoutput and narrow range of colored illumination limited the LEDutilization role to specialized applications (e.g., indicator lamps). Aslight output improved, LED utilization within other lighting systems,such as within LED “EXIT” signs and LED traffic signals, began toincrease. Over the last several years, the white light output capacityof LEDs has more than tripled, thereby allowing the LED to become thelighting solution of choice for a wide range of lighting solutions.

LEDs exhibit significantly optimized characteristics, such as sourceefficacy, optical control and extremely long operating life, which makethem excellent choices for general lighting applications. LEDefficiencies, for example, may provide light output magnitudes up to 200lumens per watt of power. Energy savings may, therefore, be realizedwhen utilizing LED-based lighting systems as compared to the energyusage of, for example, incandescent, halogen, compact fluorescent andhigh-intensity discharge (HID) lighting systems. As per an example, anLED-based lighting fixture may utilize a small percentage (e.g., 15-20%)of the power utilized by a halogen-based lighting system, but may stillproduce an equivalent magnitude of light.

While HID lighting systems have been the predominant choice forconventional horticultural lighting applications, LED technologies aregaining attraction due to their high luminous efficacy and their abilityto produce narrow-band spectral distributions. Current LED-basedhorticultural lighting systems, however, fail to produce adequate lightuniformity for indoor horticulture facility applications where naturallight is not present nor do they produce adaptable spectral tuning. Inaddition, conventional LED-based horticultural lighting systems producelight rays exhibiting decreased intensity with increasing emission anglerelative to the optical axis. Accordingly, none of the control systemsused to effect adequate light distribution characteristics, spectraltuning and power efficiency are in existence either.

Efforts continue, therefore, to develop an LED lighting system andassociated controls that exceed the performance parameters ofconventional horticultural lighting systems.

SUMMARY

To overcome limitations in the prior art, and to overcome otherlimitations that will become apparent upon reading and understanding thepresent specification, various embodiments of the present inventiondisclose methods and apparatus for the control and production ofLED-based lighting for indoor horticultural systems. Such systems mayproduce specific light intensities using a time division multiple accesscurrent sharing technique or may produce the same light intensitiesusing direct current drive to increase efficacy while utilizingalternate techniques to match a cumulative forward voltage of aparticular LED string to cumulative forward voltages of one or more LEDstrings that may be connected in parallel.

In accordance with one embodiment of the invention, a light fixturecomprises a plurality of LED channels coupled to a current node andconfigured to receive a current signal from the current node. One of theplurality of LED channels includes a first portion of LEDs having afirst forward voltage and a second portion of LEDs have a second forwardvoltage, the first forward voltage being greater than the second forwardvoltage. The light fixture further includes a shunt device coupled toeach of the first portion of LEDs and a processor coupled to each shuntdevice and configured to reduce the current signal conducted by thefirst portion of LEDs by controlling a conductivity state of each shuntdevice.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects and advantages of the invention will become apparentupon review of the following detailed description and upon reference tothe drawings in which:

FIG. 1 illustrates an LED-based horticultural light in accordance withone embodiment of the present invention;

FIGS. 2A and 2B illustrate a lens array in accordance with oneembodiment of the present invention;

FIG. 3 illustrates a cross-section of an LED/lens pair in accordancewith one embodiment of the present invention;

FIGS. 4A and 4B illustrate an intensity distribution and shadedilluminance plot in accordance with one embodiment of the presentinvention;

FIGS. 5A and 5B illustrate a conventional intensity distribution andshaded illuminance plot resulting from a bare LED without a lens or anLED with a standard Lambertian optic;

FIG. 6 illustrates a cross-section of an LED/lens pair in accordancewith an alternate embodiment of the present invention;

FIGS. 7A and 7B illustrate an intensity distribution and shadedilluminance plot in accordance with an alternate embodiment of thepresent invention;

FIG. 8 illustrates a horticulture system in accordance with oneembodiment of the present invention;

FIG. 9 illustrates an LED-based horticultural light in accordance withan alternate embodiment of the present invention;

FIG. 10 illustrates a block diagram of a power supply that may be usedwith the LED-based horticultural light of FIG. 9;

FIG. 11 illustrates a lighting system in accordance with one embodimentof the present invention;

FIG. 12 illustrates flow diagrams in accordance with several embodimentsof the present invention;

FIG. 13 illustrates a lighting system in accordance with an alternateembodiment of the present invention;

FIG. 13A illustrates a lighting system in accordance with an alternateembodiment of the present invention;

FIG. 13B illustrates I-V characteristic curves of certain LEDsimplemented within the lighting system of FIG. 13A;

FIG. 14 illustrates flow diagrams in accordance with several alternateembodiments of the present invention;

FIGS. 15A, 15B, 15C, 15D and 15E illustrate timing diagrams inaccordance with several embodiments of the present invention;

FIG. 16 illustrates an indoor horticultural system in accordance withone embodiment of the present invention;

FIG. 17 illustrates a schematic diagram that extracts power from aportion of an LED string to implement an auxiliary function inaccordance with one embodiment of the present invention;

FIG. 18 illustrates an LED-based horticultural light in accordance withan alternate embodiment of the present invention;

FIG. 19A illustrates internal portions of the LED-based horticulturallight of FIG. 18;

FIGS. 19B-19C illustrate top and bottom orthographic views of theoptical pucks of the LED-based horticultural light of FIG. 18;

FIG. 20 illustrates light distributions from horticultural lightingfixtures that do not include optical lenses in accordance with analternate embodiment of the present invention;

FIG. 21 illustrates cooling features of the LED-based horticulturallighting fixtures in accordance with various embodiments of the presentinvention; and

FIG. 22 illustrates cooling features of the LED-based horticulturallighting fixtures in accordance with various embodiments of the presentinvention.

DETAILED DESCRIPTION

Generally, the various embodiments of the present invention are appliedto a light emitting diode (LED) based lighting system that may containan array of LEDs and an array of associated lenses. The LED array may bemechanically and electrically mounted to a PCB having control and biascircuitry that allows specific sets (e.g., channels or strings) of LEDsto be illuminated on command. Any set of one or more LEDs may be groupedinto one or more channels, such that specific rows, columns or otherarrangements of LEDs in the LED array may be illuminated independentlydepending upon the specific channel within which the LED or LEDs aregrouped. A channel of LEDs may include non-linear arrangements, such assquare, circular, rectangular, zig-zag or star-shaped arrangements toname only a few. An associated lens array may be mounted in proximity tothe LED array in such a way that the lens array may perform more thanone function. For example, the lens array may mechanically impose auniform pressure onto the PCB against the associated heat sink tooptimize heat transfer from the PCB to the heat sink. Further, the lensarray may contain individual lenses with mechanical standoffs so as tomaintain an optimal separation distance between the LED and associatedlens so that light rays generated by each individual LED may beoptically varied before projection onto a target.

The mechanical standoffs may, for example, exhibit a shape (e.g.,circular) having a dimension (e.g., circumference) that is slightlylarger than a dimension (e.g., a circumference) of the LED's footprintas mounted on its associated PCB. Accordingly, as the lens array ispressed against the PCB, each mechanical standoff of each lens of thelens array may impose a substantially uniform pressure along a circularperimeter surrounding the LED to further enhance heat transfer from theLED to the heat sink.

Each lens of the lens array may, for example, be placed in suchproximity to its corresponding LED so as to collect substantially all ofthe light generated by its associated LED and virtually none of thelight generated by neighboring LEDs. Each lens may optically vary (e.g.,refract) the light distributed by its associated LED into an opticallyvaried light distribution, such that the light distributed by the lensmay exhibit a modified intensity distribution as compared to theintensity distribution of light generated by a bare LED. In alternateembodiments, multiple LEDs may be associated with a single lens suchthat the intensity of light generated by each of the multiple LEDs maybe modified by the single lens.

The Full Width Half Maximum (FWHM) beam angle may be defined as the beamangle where the light distribution exhibits an intensity equal to halfthe peak intensity. A conventional LED may exhibit an FWHM beam angle ofabout 120 degrees, where the peak intensity of light distribution mayexist at a zero-degree offset from the optical axis of the LED (e.g.,centerbeam). Each lens of the lens array may, however, modify theintensity distribution, such that the FWHM beam angle may either be lessthan, or substantially the same as, the FWHM beam angle produced by abare LED, but the intensity distribution may be modified by the lenssuch that the peak intensity may not exist at centerbeam, but rather maybe offset from centerbeam.

In one example, the intensity distribution of a bare LED may exhibit arelatively wide FWHM beam angle (e.g., a 120-degree FWHM beam angle)having a peak intensity at centerbeam. A lens of the lens array may, forexample, be used to substantially refract the FWHM beam angle of thebare LED between about 100 degrees and 140 degrees (e.g., betweenapproximately 115 degrees and 128 degrees), but may alter the intensitydistribution such that the peak intensity may not exist at centerbeam,but instead may exist at an offset between about 40 and 60 degrees(e.g., between approximately 50 and 55 degrees) half angle fromcenterbeam.

As per another example, a lens of the lens array may be used tosubstantially reduce the FWHM beam angle of the bare LED from about 120degrees to between about 50 degrees and 90 degrees (e.g., betweenapproximately 65 degrees and 75 degrees) and may further alter theintensity distribution such that the peak intensity may not exist atcenterbeam, but instead may exist at an offset between about 15 and 35degrees (e.g., between approximately 20 and 28 degrees) half angle fromcenterbeam.

Generally, each lens of the lens array may distribute light into a rayset that exhibits varying intensity depending upon the angle that eachlight ray of the projected ray set exhibits relative to a referenceaxis. For example, a reference axis of the LED may be defined as theaxis that is orthogonal to the surface of the PCB to which the LED ismounted and each light ray emitted by the LED may be refracted by thelens to exhibit an intensity that is proportional to the angle that therefracted light ray forms with respect to the reference axis. In oneembodiment, refracted light rays at lower angles relative to thereference axis may exhibit lower intensities while refracted light raysat higher angles relative to the reference axis may exhibit relativelylarger intensities.

Refracted light rays incident upon a target surface may similarly bedefined with respect to the reference axis. For example, light raysrefracted by the lens that exhibit a zero-degree offset from thereference axis may be described as exhibiting a zero-degree incidenceangle. Similarly, light rays refracted by the lens that exhibitnon-zero-degree offsets from the reference axis may be described asexhibiting incidence angles greater than zero as measured relative tothe reference axis.

A lens may be configured to refract light rays emitted by the LED toexhibit intensities that are proportional to their respective incidenceangles. For example, refracted light rays with lower incidence anglesmay exhibit lower intensities as compared to refracted light rays withhigher incidence angles. The lens may be further configured tosubstantially prohibit refraction of light rays exhibiting incidenceangles greater than a reference angle.

The lens, therefore, may produce lower intensity light rays having lowerincidence angles as compared to the intensity of light rays havingrelatively higher incidence angles. Such a lens may be particularlyuseful when the beam is to be projected onto a flat surface target witha substantially uniform illuminance across the entire illuminatedsurface regardless of the angle of incidence, or when the beam is to beprojected onto a flat surface target with an increasing illuminanceacross the entire illuminated surface as the angle of incidenceincreases. Such a lens may be further useful when the beam is to beprojected not only onto a flat surface below the light, but also ontoobjects that are adjacent to the flat surface at higher incidence angleswith respect to the light.

Stated differently, since target illuminance is proportional to theintensity of the projected light ray and inversely proportional to thesquare of the distance between the target and the lens that is producingthe projected light ray, a lens that produces light rays havingintensities that are proportional to the angle of incidence up to athreshold angle may be used to produce substantially even or uniformilluminance on a flat plane across the full beam width. That is to sayin other words, that as the angle of incidence of light rays projectedby the lens increase, so does their intensity. Furthermore, byincreasing the intensity of the light rays in proportion to the squareof the distance between the lens and the target, a substantially eventarget illuminance may be projected across the entire illuminated flatsurface regardless of the angle of incidence of light rays onto thetarget, or an illuminance may be projected onto a flat surface thatincreases with the angle of incidence. Adjacent targets may also beilluminated by light rays that do not illuminate the flat surface due totheir higher angles of incidence, but due to the higher intensity ofsuch light rays, may illuminate such adjacent targets with substantiallyequal illuminance, or with substantially increasing illuminance, ascompared to those light rays that are incident on the flat surface.

It should be noted that the advantages obtained by using thehorticultural lights in accordance with the present invention do notexist with conventional horticultural lights, which may includeLED-based horticultural lights as well. For example, conventionalhorticultural lights typically use a very small, yet high power lightsource with a secondary reflector in order to obtain a particulardistribution of light onto a typical grow bed. Such a light source,however, produces non-reflected light rays directly from the lightsource having increased intensity at centerbeam, which in turn requiresincreased vertical distance between the horticultural light and thecanopy of plants below the horticultural light.

Alternately, smaller LED-based horticultural lights may be used, but areused in very large numbers so as to obtain a projection areasubstantially equal to that of the larger conventional horticulturallights. While reduced vertical distance between the smaller LED-basedhorticultural lights and the plant canopy may be achieved,cross-lighting becomes virtually non-existent and the amount of lightprojecting throughout the depth of the plant canopy is significantlyreduced.

Accordingly, even when a particular coverage area is achieved, theilluminance projected onto the grow bed lacks uniformity and, therefore,includes “hot spots” and “dim spots” and generally provides unevenprojected illuminance due to the inverse square law as discussed in moredetail below. As discussed above, for example, conventionalhorticultural lights generally project maximum intensity at zero to lowangles of incidence, which requires relatively large vertical distancesto be established between the conventional horticultural light and theunderlying plant. As a result, vertical distances between theconventional horticultural light and the corresponding plant must bemaximized to, for example, prevent plant burn.

Horticultural lights in accordance with the present invention, on theother hand, utilize a dense array of lenses that optically vary theintensity of the light distributed by an associated array of LEDs toproject a uniform illuminance across a large surface area of a flatplane, or to project an increasing illuminance as the angle of incidenceincreases from centerbeam, despite the effects of the inverse square law(e.g., regardless of the increased distances that the light travels tothe target due to the increased angles of incidence). Accordingly, notonly may the light projection area from each horticultural light fixturein accordance with the present invention be increased as compared toconventional horticultural lights, but the illuminance within theilluminated area may be made substantially uniform, or substantiallyincreasing as incidence angles increase from centerbeam outward, aswell. In addition, the illuminance projected onto secondary targets thatare adjacent to the primary target may also be made to be substantiallyuniform, or substantially increasing as incidence angles increase fromcenterbeam outward, due to the increased intensity of light raysprojected by the horticultural light fixture at angles that are incidentupon the secondary targets.

In other embodiments, horticultural lights in accordance with thepresent invention may utilize other techniques, with or without optics,to vary light intensity. Variability of the light output (e.g., spectralvariability) may be controlled, for example, using any number of wiredprotocols including 0-10V, I2C, digital multiplex (DMX), ethernet ordigital addressable lighting interface (DALI) to name only a few. Inaddition, spectral variability may be achieved via wireless protocols,such as via ZigBee, Wi-Fi, Bluetooth or a thread-based mesh network,along with other wireless protocols. Furthermore, by combiningbroad-spectrum white LEDs with a combination of other LEDs may allow thehorticultural light to produce photosynthetically active radiation(PAR).

For example, two or more sets of broad-spectrum LEDs may be utilizedalong with one or more sets of fixed-color LEDs (e.g., one set of blueLEDs and one set of red LEDs) in order to implement broad-spectrumillumination that may better simulate sun light. In addition, the two ormore sets of broad-spectrum LEDs may exhibit different correlated colortemperatures (CCT), such that once varying intensities of the lightgenerated by both sets of broad-spectrum LEDs is mixed, a tunable CCTcomposite spectrum may result that may better simulate the variousphases of the sun, may better simulate sunlight at the various latitudesthat the sun may assume and may better simulate sun light across each ofthe four seasons.

In addition, the intensities of multiple horticultural lighting fixturesmay be controlled within an indoor grow facility to better simulate theposition of the sun throughout the daylight hours. For example, byincreasing the intensity of easterly-positioned horticultural lightingfixtures in the morning hours may better simulate the rising sun, byincreasing the intensity of centrally-positioned horticultural lightingfixtures during the mid-day hours may better simulate themid-morning/mid-afternoon sun and by increasing the intensity ofwesterly-positioned horticultural lighting fixtures in the lateafternoon/evening hours may better simulate the setting sun.

Horticultural lighting fixtures utilized within a greenhouse may also beutilized to augment the light produced within the greenhouse. As anexample, a sensor may measure various aspects of light generated withinthe greenhouse and may provide the measurements to a controller. Thecontroller may then compare the measurements with light recipescontained within a light prescription database to determine whether anydeficiencies exist within the greenhouse light (e.g., deficiencies incolor spectrum, color temperature, photosynthetic photon flux, etc.). Ifso, the controller may activate one or more channels of LEDs within thelight fixture to augment the greenhouse light, thereby filling indeficiencies detected in the greenhouse light (e.g., increasingintensity of a particular spectrum of light, increasing photosyntheticphoton flux, varying color temperature, etc.). If the light generatedwithin the greenhouse already conforms to a particular light recipe, onthe other hand, then the controller may deactivate the light fixturesaltogether to save energy.

In one embodiment, each set of the multiple sets of LEDs may be arrangedas independent channels of LEDs, where each channel of LEDs may beindependently operated at a selected intensity based upon a magnitude ofcurrent that may be conducted by each channel of LEDs. The controlcircuitry that may be used to select the magnitude of current that maybe conducted by each channel of LEDs may be integrated within the powersupply that may also contain the bulk power conversion (e.g.,alternating current (AC) to direct current (DC) and/or DC to DC powerconversion electronics) and regulation (e.g., constant currentregulation or constant voltage regulation) electronics.

Turning to FIG. 1, horticultural light 100 is exemplified, which mayinclude one or more lens arrays (e.g., lens array 118 and 126). Eachlens array may include one or more rows of lenses (e.g., four rows oflenses) and one or more columns of lenses (e.g., 12 columns of lenses).One or more LEDs (not shown) may be included behind each lens (e.g.,lens 102) so that in one example, the number of LEDs included withinhorticultural light 100 may be equal to the number of lenses included ineach lens array (e.g., 48 LEDs per lens array for a total of 96 LEDs perhorticultural light 100). As per another example, multiple LEDs (e.g.,one red, one green, one blue and one white LED from each RGBW channel ofLEDs) may be included behind each lens and may further be rotated withrespect to one another so as to smooth the light distribution projectedby each multiple LED/single lens combination. In one embodiment, forexample, each of 4 LEDs combined under a single lens may be attached tothe underlying PCB at 0 degree, 45 degree, 90 degree and 135 degreeoffsets, respectively, whereby the magnitude of angle offset may beinversely proportional to the number of LEDs combined under a singlelens (e.g., 180 degrees/4 equals a rotation offset of 45 degrees fromone LED to the next).

Bezel 134 may, for example, provide a substantially constant pressurearound a perimeter of horticultural light 100 to, for example, seal asubstantially transparent media to horticultural light 100 therebymaintaining horticultural light 100 in a water proof/water resistantstate. The transparent media may also press the lens array against thePCB behind the lens array, such that substantially 100% of the lightgenerated by each LED may be directed through its respective lens andthrough the transparent media to prohibit virtually any of the lightfrom being redirected back into horticultural light 100. While thedimensions (e.g., 4.5 inches wide×22 inches long) of horticultural light100 may be significantly smaller than conventional LED horticulturallights (e.g., 4 feet wide×4 feet long), horticultural light 100 via itsdense array of LEDs and associated lenses may nevertheless project asubstantially equivalent amount of light onto a conventional grow bed,but may do so with substantially uniform illuminance, or substantiallyincreasing illuminance from centerbeam outward, across the entire growbed and adjacent grow beds unlike the substantially non-uniformilluminance, or substantially decreasing illuminance from centerbeamoutward, as projected by conventional horticultural lights.

Horticultural light 100 may further include control circuitry (e.g.,controllers 110, 112, 114 and 116) and associated circuitry (e.g., biascircuitry 124) such that any one or more LEDs (not shown) may beindependently transitioned into conductive and non-conductive states oncommand. Alternately, LED control and bias circuitry (e.g., controllers110, 112, 114, 116 and associated bias control circuitry 124) may not beco-located on the same PCB to which the associated LEDs are mounted, butmay instead be located remotely to the PCB (e.g., on a modular controland bias circuit that may be interchangeably introduced intohorticultural light 100 or into a bias and control bus that connects twoor more horticultural lights 100 together).

In one embodiment, the conductive state of any multiple of LEDs (e.g.,the LEDs, not shown, behind each row of lenses 126, 128, 130 and 132)may be independently controlled. In other embodiments, the conductivestate of any multiple of LEDs (e.g., the LEDs, not shown, behind eachcolumn of each array of lenses 118 and 126) may be independentlycontrolled. Once an LED (not shown) is transitioned to its conductivestate, the associated lens (e.g., lens 102) may produce a lightdistribution that may exhibit a particular intensity profile, which mayproduce a substantially uniform target illuminance, or a substantiallyincreasing target illuminance from centerbeam to the edge of the beampattern, across a flat surface as discussed in more detail below.

Multiple horticultural lights 100 may be employed for use ashorticultural lighting in a greenhouse, small indoor grow room, or in acommercial production facility as part of an integrated horticulturalsystem. Horticultural light 100 may, for example, replicate naturallight that may be absent in an indoor grow facility and may becontrolled (e.g., via bias controller 124 and controllers 110, 112, 114and 116) to deliver virtually any wavelength of light that may beproduced by an LED, at virtually any intensity, at virtually any dutycycle that may be useful in a horticultural facility. Furthermore,virtually any mixture of LEDs may be utilized within horticultural light100 to produce a wide range of color temperature, spectrum and colorrendering index (CRI).

As an example, each channel of LEDs (e.g., rows of LEDs, not shown,behind rows of lenses 126, 128, 130 and 132, respectively) may eachinclude a selection of LEDs that may produce a range of colortemperature and CRI attributes. For example, the rows of LEDs (notshown) behind lens rows 126 and 128 may include LEDs exhibiting a colortemperature of approximately 3000° K and a CRI greater than 90. Asanother example, the row of LEDs (not shown) behind lens row 130 mayinclude LEDs exhibiting a color temperature of approximately between5700° K and 6500° K and may exhibit a CRI less than 80. As per anotherexample, the row of LEDs (not shown) behind lens row 132 may includeLEDs exhibiting a narrow-bandwidth red color spectrum (e.g., at or below1800° K or between 580 nm and 750 nm). It should be noted that virtuallyany combination of wavelength, color temperature, spectrum and CRI maybe used to match the particular photosynthetic and photomorphogenicrequirements of the crop of interest.

It should be further noted that the LEDs (not shown) may include apercentage (e.g., 75%) of phosphor converted white LEDs and a percentage(e.g., 25%) of narrow band red or blue spectrum LEDs, such as aluminumgallium indium phosphide (AlGaInP) LEDs. Alternately, for example,phosphor converted red LEDs may also be used, which may facilitate theuse of indium gallium nitride (InGaN) LEDs exclusively, both for thephosphor converted white LEDs and the phosphor converted red LEDs. Suchan arrangement of matched InGaN LEDs may, for example, provide a verybroad spectrum white light with an emphasis on the blue and red spectrawhile also providing uniform thermal performance and degradation as wellas the advantage of facilitating the implementation of strings ofmultiple LEDs (e.g., the string of LEDs, not shown, behind lens rows126, 128, 130 and 132) that may be arranged serially with asubstantially constant forward voltage.

As discussed in more detail below, bias controller 124 may include wiredand/or wireless access control systems, such as Bluetooth, Wi-Fi,thread-based mesh, digital multiplex (DMX), I2C, ethernet ortelecommunications-based control systems that may allow horticulturallight 100 to be controlled remotely, either within the same facility, orvia a regional or national control room. Accordingly, the lighting ofone or more unmanned horticultural facilities may be centrallycontrolled by a single control station. Such a control station, forexample, may also control other aspects of the horticultural facility.Air filtration and circulation systems, for example, may require remoteaccess control for heat and exhaust mitigation. Various irrigationsystems, such as drip irrigation, hydroponic flood benches and troughbenches along with a nutrient management system may also be controlledby the control station. In general, the control station may not onlycontrol the one or more horticultural lights 100 of the horticulturalfacility, but also the nutrients, air circulation, irrigation,dehumidification, carbon dioxide (CO₂) injection and other facilitiesthat may be required to maintain the exact environment needed by thevarious growing rooms, cloning rooms and flowering rooms of thehorticultural facility.

Turning to FIGS. 2A and 2B, a front view and a rear view, respectively,of a lens array (e.g., lens array 118 of FIG. 1) are exemplified.Mechanical portions 202 and 204, for example, of the lens array may notinclude any optical attributes, but may instead provide a frameworkwithin which optical portions (e.g., lenses 206) may be configured intoan array (e.g., multiple rows and columns of lenses 206). Mechanicalportions 202 and 204 may, for example, include mounting features (e.g.,apertures 208) that may facilitate the insertion of mounting hardware(e.g., screws) that may be used to mount the lens array to theunderlying PCB and lighting fixture housing/heat sink (not shown). Byutilizing such mounting hardware, mechanical portion 204 may be pressedagainst the underlying PCB and LEDs (not shown), which may in turn pressthe underlying PCB against the housing/heat sink (not shown) of thehorticultural light (e.g., horticultural light 100) so as to promoteeffective conduction of heat away from the LEDs.

Mechanical portion 204 may further include raised portions 210 that maybe used to create an optimal separation distance between the lens arrayand the underlying LED array (not shown). Indented portions 212 may, forexample, accommodate the insertion of at least a portion of an LEDpackage (e.g., the dome portion of an LED package). The height of raisedportions 210 may be selected to create an optimal separation distancebetween the optical input portion of the lens (e.g., lens 206) and theassociated LED (not shown) that is inserted into the correspondingindented portion 212 of lens 206 as discussed in more detail below.Raised portions 210 may exhibit a particular geometric shape (e.g.,circular) so as to match a particular foot print of each LED (not shown)of the LED array. As such, raised portions 210 may impose asubstantially uniform pressure surrounding, and in close proximity to,each associated LED (not shown) so as to create a uniform conductionpath so that heat may be conducted away from the LED through theassociated PCB and heat sink, thereby improving the performance of theLED.

In one embodiment, the array of lenses 206 may be arranged as an arrayof rows and columns of lenses, where each lens may exhibit a circularshape having a diameter (e.g., 13 mm diameter) and a separation distancefrom each neighboring lens (e.g., a separation distance of 16 mm centerto center). The composition of the array of lenses 206 may be that of anoptical grade polymer (e.g., acrylic) that may exhibit an index ofrefraction of between about 1.48 and 1.5 (e.g., approximately 1.491) orthat of an optical grade polycarbonate that may exhibit an index ofrefraction of between about 1.5 and 1.7 (e.g., approximately 1.58).

Turning to FIG. 3, a cross-sectional view is exemplified in which LEDpackage 306, having hemispherical dome portion 312, may protrude intoindented portion 304 of lens 314. It should be noted that indentedportion 304 may exemplify a cross-section of a lens array (e.g., across-section of indented portion 212 of the lens array of FIG. 2) whereindented portion 304 may include optical input 308 to lens 314 that mayaccept the light distribution from LED package 306 into lens 314.Protrusion 302 may exemplify a cross-section of a lens array (e.g., across-section of mechanical portion 210 of the lens array of FIG. 2)where protrusion 302 includes surface area 316 that may be incommunication with a PCB (not shown) to select an optimal separationdistance (e.g., separation distance 318) between the LED deck (e.g., PCB326 of LED package 306) and optical input 308 to lens 314. In oneembodiment, separation distance 318 may be between about 0.3 mm andabout 0.4 mm (e.g., approximately 0.35 mm).

Portion 310 may exemplify a cross-section of a lens array (e.g., across-section of lens 206 of FIG. 2) where portion 310 may be theoptical output of lens 314 that produces the optically varied (e.g.,refracted) light distribution. Light distribution from lens 314 mayexhibit an optical axis (e.g., axis 320) that may be orthogonal to themounting surface of the PCB (not shown) to which LED package 306 ismounted. In addition, the projected light distribution from lens 314 maybe described in terms of the intensity of each ray and its geometricorientation with respect to axis 320 as well as the projectedilluminance onto a flat plane and projected illuminance onto targetsadjacent to the flat plane.

It should be noted that the lens array is configured such that aprojected light distribution from an individual lens (e.g., lens 314) ofthe lens array may not be incident upon adjacent lenses (e.g., lenses326 and 328) of the lens array. In one embodiment, for example, lens 314may refract the light distribution of LED 306 into a half-beam anglebetween about 50 degrees and 90 degrees (e.g., between approximately 65degrees and 75 degrees) having full-beam width 322 that is not incidenton any adjacent lenses (e.g., lenses 326 and 328).

Turning to FIG. 4A, a light distribution is exemplified that may beproduced by an LED/lens combination in accordance with one embodimentthat may include an LED (e.g., LED package 306 of FIG. 3) and a lens(e.g., lens 314 of FIG. 3) to produce a light distribution asexemplified in FIG. 4A. As illustrated, for example, the lightdistribution from lens 314 may exhibit a center beam intensity (e.g.,about 77 candela) at a zero-degree offset from the optical axis (e.g.,axis 320 of FIG. 3). The light distribution from lens 314 may exhibit apeak intensity (e.g., 84 candela) offset from the center beam by anangle of about 22.5 degrees to about 27.5 degrees.

It can be seen, therefore, that if the light distribution of FIG. 4A isprojected onto a target having a flat surface by a lens (e.g., lens 314of FIG. 3), the distance between the lens and the target changesdepending upon the angle of incidence of the light distribution onto thetarget. As an example, if the angle subtended by a light ray is offsetfrom the optical axis (e.g., axis 320 of FIG. 3) by zero degrees, thenthe distance traveled by the light ray to the target is at its minimalvalue. As the angle subtended by a light ray referenced to the opticalaxis increases, so does the distance that the light ray must travelbefore being incident onto the target's surface.

According to the inverse square law, therefore, the target illuminancedecreases in proportion to the inverse square of the distance betweenthe lens and the target, thereby causing the target illuminance todecrease with increasing beam width. However, since the intensity of thelight distribution of FIG. 4A increases with increasing beam angle up toa reference beam angle (e.g., between about 22.5 degrees to about 27.5degrees), the target illuminance may nevertheless remain substantiallyuniform, or may substantially increase with increasing beam angle,despite the effects of the inverse square law as exemplified, forexample, in the associated shaded illuminance plot of FIG. 4B. Inaddition, for example, since the intensity of light distribution ismaximum at maximum beam angle, the effective distance of the illuminanceonto targets adjacent to the main target may be extended, such as may bethe case when projecting light through side portions of the canopies ofadjacent plants.

As a comparison, FIG. 5A exemplifies an intensity distribution from abare LED (e.g., an LED without an optically varied distribution found onconventional horticultural lights) and FIG. 5B exemplifies theassociated shaded illuminance plot. As can be seen from FIG. 5A, theintensity peaks at centerbeam (e.g., zero-degree offset from the LED'soptical axis) and then decreases with increasing beam angle, whichcauses the illuminance, as exemplified by the shaded illuminance plot ofFIG. 5B, to be non-uniform and decreasing in proportion to the inverseof the square of the increasing distance between the LED and itsillumination target. It can be seen, therefore, that without the opticaldistribution of a lens in accordance with the various embodiments of thepresent invention, uniform illuminance onto a flat target is notpossible. Rather, decreasing illuminance with increasing angles ofincidence is produced.

Turning to FIG. 6, a cross-sectional view of an alternate LED/lensembodiment exhibiting a wider beam angle is exemplified in which LEDpackage 606, having hemispherical dome portion 612, may protrude intoindented portion 604 of lens 614. It should be noted that indentedportion 604 may exemplify a cross-section of a lens array (e.g., across-section of indented portion 212 of the lens array of FIG. 2) whereindented portion 604 includes optical input 608 to lens 614 that acceptsthe light distribution from LED 606 into lens 614. Protrusion 602 mayexemplify a cross-section of a lens array (e.g., a cross-section ofmechanical portion 210 of the lens array of FIG. 2) where protrusion 602includes surface area 616 that may be in communication with a PCB (notshown) to select an optimal separation distance (e.g., separationdistance 618) between the LED deck (e.g., PCB 626 of LED package 606)and optical input 608 to lens 614. In one embodiment, separationdistance 618 may be between about 0.3 mm and about 0.4 mm (e.g.,approximately 0.35 mm).

Portion 610 may exemplify a cross-section of a lens array (e.g., across-section of lens 206 of FIG. 2) where portion 610 may be theoptical output of lens 614 that produces the optically varied (e.g.,refracted) light distribution. Light distribution from lens 614 mayexhibit an optical axis (e.g., axis 620) that may be orthogonal to themounting surface of the PCB (not shown) to which LED package 606 ismounted. In addition, the projected light distribution from lens 614 maybe described in terms of the intensity of each ray and its geometricorientation with respect to axis 620 as well as the projectedilluminance onto a flat plane and the projected illuminance onto targetsadjacent to the flat plane.

It should be noted that the lens array is configured such that aprojected light distribution from an individual lens (e.g., lens 614) ofthe lens array may not be incident upon adjacent lenses (e.g., lenses626 and 628) of the lens array. In one embodiment, for example, lens 614may refract the light distribution of LED 606 into a beam angle betweenabout 100 degrees and 140 degrees (e.g., between approximately 115degrees and 128 degrees) having beam width 624 that is not incident onadjacent lenses 626 and 628.

Turning to FIG. 7A, a light distribution is exemplified that may beproduced by an LED/lens combination in accordance with an alternateembodiment that may include an LED (e.g., LED package 606 of FIG. 6) anda lens (e.g., lens 614 of FIG. 6) to produce a light distribution asexemplified in FIG. 7A. As illustrated, for example, the lightdistribution from lens 614 may exhibit a center beam intensity (e.g.,about 20 candela) at a zero-degree offset from the optical axis (e.g.,axis 620 of FIG. 6). The light distribution from lens 614 may exhibit apeak intensity (e.g., 59 candela) offset from the center beam by anangle of about 50 degrees to about 55 degrees (e.g., approximately 54degrees).

It can be seen, therefore, that if the light distribution of FIG. 7A isprojected onto a target having a flat surface by a lens (e.g., lens 614of FIG. 6), the distance between the lens and the target changesdepending upon the angle of incidence of the light distribution onto thetarget. As an example, if the angle subtended by a light ray is offsetfrom the optical axis (e.g., axis 620 of FIG. 6) by zero degrees, thenthe distance traveled by the light ray to the target is at its minimalvalue. As the angle subtended by a light ray referenced to the opticalaxis increases, so does the distance that the light ray must travelbefore being incident onto the target's surface.

According to the inverse square law, therefore, the target illuminancedecreases in proportion to the inverse square of the distance betweenthe lens and the target, thereby causing the target illuminance todecrease with increasing beam width. However, since the intensity of thelight distribution of FIG. 7A increases with increasing beam angle up toa reference beam angle (e.g., about 54 degrees), the target illuminancemay nevertheless remain substantially uniform, or may substantiallyincrease with increasing beam angle, despite the effects of the inversesquare law as exemplified, for example, in the associated shadedilluminance plot of FIG. 7B. In addition, for example, since theintensity of light distribution is maximum at maximum beam angle, theeffective distance of the illuminance onto targets adjacent to the maintarget may be extended, such as may be the case when projecting lightthrough side portions of the canopies of adjacent plants.

In comparing the intensity distribution plots of FIGS. 4A and 7A, it canbe seen that lens 314 of FIG. 3 produces a greater peak intensity thanthe peak intensity produced by lens 614 of FIG. 6. Furthermore, sincethe beam angle produced by lens 614 of FIG. 6 is wider than thatproduced by lens 314 of FIG. 3, the area illuminated by lens 614 may begreater than the area illuminated by lens 314, but the illuminanceproduced by lens 614 may be less than that produced by lens 314 giventhe same distance to target. Accordingly, while the number ofhorticultural lights (e.g., horticultural lights 100 of FIG. 1)utilizing lens 614 needed to illuminate a given target area may be lessthan the number of horticultural lights utilizing lens 314 needed toilluminate the same target area, horticultural lights utilizing lens 614may be mounted closer to the target area to achieve the same illuminancegenerated by horticultural lights utilizing lens 314 that are mountedfurther away from the target area. Accordingly, less vertical distancebetween the horticultural light and the associated grow bed may beneeded when utilizing lens 614, thereby allowing multiple levels of growbeds to be established floor to ceiling within the indoor horticulturalfacility.

Turning to FIG. 8, horticultural system 800 is exemplified includinghorticulture light 804, which may include a lens array (e.g., lens array118 and 126 as exemplified by horticulture light 100 of FIG. 1). Inalternate embodiments, horticulture light 804 may not include a lensarray, or may use a different lens array layout. In addition,horticultural system 800 may include grow beds 808, 808A and 808B thatmay be used to cultivate virtually any crop that may be grown within ahorticulture facility (e.g., a greenhouse). Horticultural lightingsystem 800 may further include, for example, quantum sensor 806, whichmay include a photosynthetically active radiation (PAR) sensor having auniform sensitivity to PAR light, a light meter to measure instantaneouslight intensity and/or a data logger to measure cumulative lightintensity. Quantum sensor 806 may, for example, provide spectrographicdata, which may include correlated color temperature (CCT), CRI,chromaticity and photosynthetic photon flux (PPF) associated withhorticulture light 804 and any ambient light that may be incident uponquantum sensor 806 (e.g., ambient light 830 as may be provided within agreenhouse that may be incident upon grow beds 808, 808A and 808B) amongother spectrographic data.

In one embodiment, controller 802 may access a database (e.g., lightprescription database 814), which may include predetermined lightprescriptions for controlling the light output from horticulture light804 and may then utilize interface 810 to tune horticulture light 804 inaccordance with the predetermined light prescriptions (e.g., prescribedlight intensity, CCT, PPF and color spectrum). Controller 802 andinterface 810 may, for example, be used by an operator to eithermanually tune horticulture light 804 to manual settings or tunehorticulture light 804 to predetermined light prescriptions 814.Alternately, controller 802 may automatically update horticulture light804 based upon comparisons between quantum sensor measurements 812 andlight prescriptions 814 using closed-loop feedback control so as tomaintain horticulture light 804 within operational constraints asdefined by light prescriptions 814. For example, the temperature ofhorticulture light 804 may increase, thereby increasing the temperatureof the LEDs contained within horticulture light 804, which may in turndecrease an intensity of light generated by horticulture light 804. As aresult of closed-loop feedback, the decreased intensity due to increasedtemperature may be detected by quantum sensor 806 and reported tocontroller 802, whereby controller 802 may responsively increase theintensity of the light distributed by horticulture light 804.Conversely, as discussed in more detail below, controller 802 mayinstead invoke other measures (e.g., increased air flow), which may thenlower the temperature of horticulture light 804, thereby resulting in anincreased intensity light distribution.

As per another example, quantum sensor 806 may detect ambient light(e.g., ambient light 830 provided within a greenhouse) in addition tothe light that may or may not be generated by horticulture light 804. Insuch an instance, controller 802 may automatically update horticulturelight 804 (e.g., control the PPF and/or intensity of light generatedacross the PAR spectrum) based upon comparisons between quantum sensormeasurements 812 and light prescriptions 814 using closed-loop feedbackcontrol so as to maintain horticulture light 804 within operationalconstraints as defined by light prescriptions 814.

In one embodiment, for example, light prescriptions 814 may define aparticular PPF that may be necessary to achieve an optimal electrontransport rate (ETR) within a plant (e.g., plants contained within growbeds 808, 808A and 808B), which may be dependent upon the particularspecies of plant being grown within grow beds 808, 808A and 808B. Anoptimal ETR, for example, may be achieved at lower levels of PPF for oneplant species, while higher levels of PPF may be required to achieve anoptimal ETR for another species of plant. The efficiency of theconversion of the energy of photons into electron transport may, forexample, be proportional to the exponential expression, a(1−e^(−bPPF)),where the constants “a” and “b” may be plant species dependent and “PPF”may be the photosynthetic proton flux measured in micro-moles per squaremeter per second (e.g., as measured by quantum sensor 806). Such anexponential expression may be provided within light prescriptions 814and may be utilized by controller 802 to constrain an aspect ofhorticulture light 804 (e.g., light intensity) so that the PPF receivedby the plant may result in optimized ETR.

In one example, the PPF received by a plant located within a greenhousemay already be sufficient, which may result in the deactivation ofhorticulture light 804 by controller 802. Conversely, the PPF receivedby a plant located within a greenhouse may not be sufficient, which mayresult in the activation of one or more channels of LEDs containedwithin horticulture light 804 to generate the PPF required. Accordingly,for example, controller 802 may vary the intensity of light generated bythe one or more channels of LEDs contained within horticulture light 804between 0% and 100% intensity in response to measurements 812 taken byquantum sensor 806 to generate the PPF required for optimal ETR asdictated by light prescriptions 814.

Additionally, plants may require the transfer of a threshold number ofmicro-moles of electrons per meter per day to optimize growth.Accordingly, quantum sensor 806 may record a cumulative number ofmicro-moles of photons received (e.g., from horticulture light 804 andthe ambient light produced by the greenhouse within which the plant ishoused) on a hourly/daily basis and may forward the measurements tocontroller 802 for comparison to a variable contained within lightprescriptions 814. Based on the comparison, controller 802 may vary anaspect of light generated by horticulture light 804 (e.g., intensityvariation between 0% and 100%) so that the plant may receive a propernumber of micro-moles of photons per meter per day to achieve optimizedETR for optimized growth.

In an alternate embodiment, for example, light prescriptions 814 maydefine a particular color spectrum and intensity of light distributedwithin the color spectrum that may be necessary for optimal growth ofplants contained within grow beds 808, 808A and 808B. Controller 802 maycompare measurements 812 with light prescriptions 814 to determinewhether measurements 812 conform to a particular color spectrum recipe(e.g., whether ambient light generated within the greenhouse without theuse of horticulture light 804 is sufficiently matched to the colorspectrum recipe). If not, controller 802 may tune the spectrum generatedby horticulture light 804 as discussed herein to augment the spectralgaps contained within the ambient light generated within the greenhouse.If, on the other hand, the ambient light already conforms to the colorspectrum recipe, then controller 802 may instead deactivate horticulturelight 804 to, for example, save energy.

Controller 802 may provide command and control signals to horticulturelight 804 via interface 810 (e.g., via a wired protocol such as 0-10V,I2C, DALI or DMX, or via a wireless protocol, such as ZigBee, Wi-Fi,thread-based mesh network or Bluetooth). Controller 802 may receive allmeasurement data from quantum sensor 806 and may provide such resultsvia human-machine interface (HMI) 816 to an operator of horticulturalsystem 800 so that the operator may ascertain the performancecharacteristics of horticulture light 804. It should be noted that HMI816 may either be located within the same facility as controller 802, ormay be located remotely within a regional or national control room, sothat multiple controllers 802 in multiple grow facilities may becentrally managed remotely.

As discussed above in relation to FIG. 1, horticulture light 804 mayimplement multiple arrays of LEDs, whereby each LED array may bearranged into channels (e.g., along rows and/or columns) and eachchannel of LEDs may be controlled separately and independently. In oneembodiment, horticulture light 804 (e.g., as discussed above in relationto horticulture light 100 of FIG. 1) may implement multiple channels(e.g., 4 channels) whereby each row of LEDs (e.g., rows 126, 128, 130and 132 of FIG. 1) may represent a separately and independentlycontrollable LED channel.

Horticulture light 804 may be utilized to produce broad-spectrum whitelight (e.g., between about 420 nm and about 750 nm) with variable CCT sothat the light spectrum may be tuned to better simulate various aspectsof sun light. For example, multiple phases of the sun, simulation of sunlight in all four seasons (e.g., fall, winter, spring, summer) andlatitude of the sun may be better simulated using CCT control.Furthermore, no matter what CCT value may be selected, the intensity oflight produced may be selectable as well, such that in one example,multiple CCT values may be obtained while maintaining a constantintensity.

As discussed above, horticultural light 804 may include appropriatelens/LED combinations to provide illuminance 818, where illuminance 818may be substantially uniform or may substantially increase as the angleof incidence increases with respect to optical axis 824. In addition,through increased intensity at increased beam angles as compared tooptical axis 824, light rays 820 and 822 may illuminate adjacent growbeds 808A and 808B, respectively, with increased illuminance from thesides of the respective grow beds to better simulate light received fromthe sun. Stated differently, by increasing the intensity at increasingangles of incidence as compared to optical axis 824, light generated byhorticulture light 804 may not only be effective as to grow bed 808, butalso to grow beds 808A and 808B even though grow beds 808A and 808B arefurther away from horticulture light 804 as compared to grow bed 808.

In one embodiment, horticulture light 804 may include multiple channels(e.g., two rows) of broad-spectrum white LEDs, whereby the intensity ofeach row of LEDs may be controlled by a separate channel (e.g., 1 of Nchannels 810) of controller 802. The first set of broad-spectrum whiteLEDs may, for example, exhibit a first CCT (e.g., a CCT equal to about2700K) and the second set of broad-spectrum white LEDs may exhibit asecond CCT (e.g., a CCT equal to about 5700K). Through operation ofcontroller 802, the intensity of each set of broad-spectrum white LEDsmay be controlled to create an averaged mix of light exhibiting a CCTbetween about 2700K and 5700K as may be required (e.g., as required bylight prescription 814). Alternately, each channel of broad-spectrumwhite LEDs may include mixed CCT values (e.g., both 2700K and 5700K).

In alternate embodiments, the number of channels of broad-spectrum whiteLEDs may, for example, be increased (e.g., increased to 3 channels) eachchannel exhibiting a different CCT value (e.g., 2700K, 4000K and 6000K).In such an instance, the averaged CCT value of the 3-channel combinationmay be variable between about 2700K and 6000K, but with an emphasis ofmid-range energy due to the addition of the 3rd channel (e.g., the 4000Kchannel) of broad-spectrum white LEDs. Alternately, each channel ofbroad-spectrum white LEDs may include mixed CCT values (e.g., all threeof 2700K, 4000K and 5700K).

In yet other embodiments, horticulture light 804 may include one or morechannels of fixed color LEDs (e.g., one channel of red LEDs and/or onechannel of blue LEDs) in addition to one or more channels ofbroad-spectrum white LEDs. In such an instance, even wider ranging mixedCCT values may be obtained, since the averaged CCT values produced bythe broad-spectrum white LEDs may be pushed to lower values (e.g.,through the use of the variable intensity red channel) and/or pushed tohigher values (e.g., through the use of the variable intensity bluechannel).

Even broader spectrums may be achieved, for example, when the one ormore channels of fixed color LEDs may themselves be implemented usingmultiple wavelengths. For example, a channel of red LEDs may beimplemented through use of a first proportion of red LEDs (e.g., 50% ofthe red LEDs producing light with a 660 nm wavelength) and a secondproportion of red LEDs (e.g., 50% of the red LEDs producing light with a625 nm wavelength). Additionally, a channel of blue LEDs may beimplemented through use of a first proportion of blue LEDs (e.g., 50% ofthe blue LEDs producing light with a 440 nm wavelength) and a secondproportion of blue LEDs (e.g., 50% of the blue LEDs producing light witha 460 nm wavelength). Accordingly, even broader spectrum red and bluechannels may be combined with broad-spectrum white channels to createthe broadest spectrum light possible all while also providing variableCCT.

Turning to FIG. 9, an alternate embodiment of horticulture light 900 isexemplified, in which substantially none of the bias and controlcircuitry that may be associated with each channel of LEDs is co-locatedon the same PCB as each LED. Instead, the bias and control circuitry foreach channel of LEDs (e.g., 4 channels 810 of FIG. 8) may be integratedwithin the bulk power conversion (e.g., power supply 904) that may bemounted to horticulture light 900. In addition, power supply 904 mayconvert the AC voltage (e.g., 110 VAC at 60 Hz applied via power cord902) to a wide ranging DC potential between approximately 10 VDC and 300VDC (e.g., approximately between about 12 VDC and 48 VDC). Buck, boostand/or buck/boost converters (not shown) also contained within powersupply 904 may form at least a portion of the bias and control circuitrythat may be required to illuminate each channel of LEDs contained withinhorticulture light 900 at specified intensities as may be selected via awired or wireless control interface (e.g., a wired DMX interface).

Horticulture light 900 may exhibit a longer length profile as compared,for example, to horticulture light 100 of FIG. 1. For example, a longerprofile may be obtained by concatenating two horticulture lights 910 and912 (e.g., two horticulture lights 100 of FIG. 1 end to end for twicethe length). It should be noted that the circuitry of controller areas(e.g., areas 908) that may otherwise exist within other horticulturelights (e.g., horticulture light 100 of FIG. 1) may instead be containedwithin power supply 904.

Turning to FIG. 10, a block diagram of power supply 904 of FIG. 9 isillustrated, which may include AC/DC bulk conversion block 1002 to bulkconvert an alternating current (AC) input to a direct current (DC)voltage, power management block 1004 to provide operational power formiscellaneous devices (e.g., CPU 1018 and DMX 1010) and one or moreDC-DC converters (e.g., buck, boost and/or buck/boost converters1006-1008) to, for example, provide sufficient power to vary theintensity of the one or more arrays of LEDs contained within thehorticulture light (e.g., horticulture light 900 of FIG. 9).

In one embodiment, for example, converters 1006-1008 may generate avoltage substantially equal to the forward voltage of their respectiveLED arrays and may vary the drive current according to a constantcurrent topology to achieve a desired intensity of each LED array (e.g.,as may be determined by light prescription 814 or HMI 816 of FIG. 8).The desired intensity of each LED array may, for example, be controlledvia DMX 1010 and/or I2C 1020, where each LED array may exist within thesame DMX universe and may be responsive to an 8-bit intensity controlword received within its designated DMX slot. DMX 1010 may facilitateremote device management (RDM) data handling, whereby full duplexcommunications may be accommodated to, for example, define DMX slotnumbers and to correlate those DMX slot numbers to each of therespective LED arrays.

Firmware executed by CPU 1018 may reside, for example, within memory(e.g., flash memory), which may be local to CPU 1018 or remotely locatedwith respect to CPU 1018. Firmware may, for example, be changed orupdated (e.g., boot loaded) via universal serial bus (USB) 1012 (e.g.,USB port 906 of FIG. 9). Such firmware may control, for example, powermanagement to the LED arrays as provided by converters 1006-1008. In oneembodiment, for example, firmware executed by CPU 1018 may operate DC-DCconverters 1006-1008 according to a fixed-frequency, constant currenttopology that may select a minimum and a maximum current to be conductedby each LED array through analog control. Furthermore, firmware executedby CPU 1018 may operate DC-DC converters 1006-1008 (e.g., via pulsewidth modulated (PWM) control signals) to select any number (e.g., 255)of intensity levels that may be generated by each LED array at anycurrent setting. In one example, current magnitudes between 1% and 25%of the maximum current magnitude may be PWM modulated so as to provideprecision dimming at the lowest levels of dimming (e.g., 255 levels ofdimming may be implemented via PWM modulation to achieve approximately0.1% dimming granularity between 1% and 25% of maximum current).

Firmware executed by CPU 1018 may, for example, receive telemetry data(e.g., thermal data via temperature sensors 1016) relative to, forexample, the operating temperature of the horticulture light (e.g.,horticulture light 900 of FIG. 9). In response, CPU 1018 may issue fancontrol signals (e.g., fan RPM control signals) to fan 1014 so as tomaintain horticulture light 900 within a specified temperature range. Inaddition, CPU 1018 may limit the maximum current conducted by each LEDarray as discussed above to maintain the operating temperature ofhorticulture light 900 below a maximum temperature range. For example,if the maximum temperature range is exceeded by horticulture light 900,CPU 1018 may first increase the speed at which one or more fans 1014 maybe operating, thereby providing increased air flow to horticulture light900 in an effort to lower the operating temperature of horticulturelight 900 below its maximum operating temperature. If the operatingtemperature is not reduced below the maximum temperature range, then CPU1018 may decrease the magnitude of current conducted by each LED arrayin a linear rollback fashion until the operating temperature is reducedbelow the maximum temperature range. As discussed above in relation toFIG. 8, for example, CPU 1018 may be operating in response to quantumsensor input data (e.g., quantum sensor input data that may be receivedvia I2C interface 1020), whereby intensity variations of light measuredby the quantum sensor may be compared to light prescriptions containedwithin a database and through closed-loop feedback, CPU 1018 maycounteract such intensity variations any number of ways. For example, anamount of current generated by DC-DC converters 1006-1008 may be changedto effect an intensity variation in the LED arrays. Alternately, forexample, adjusting the speed by which fan 1014 is spinning may controlthe temperature of the one or more LED arrays, which may then effectuatea change in intensity of light generated by the LED arrays, since lightintensity generated by the LED arrays may be inversely proportional tothe temperature of the LED arrays.

As discussed above, firmware received via USB 1012 may be used tocontrol certain parameters of operation of horticulture light 900 via acomputer (not shown) that may be communicating with USB 1012. Forexample, any number of DC-DC converters 1006-1008 may be activateddepending upon the number of LED arrays or channels that may existwithin horticulture light 900. For example, if eight DC-DC convertersexist within power supply 904, but only four LED arrays or channelsexist within a particular horticulture light, then half of the DC-DCconverters may be activated for operation via firmware loaded via USB1012 while the other half remain in a deactivated state. In operation,each activated DC-DC converter may receive a unique DMX address, suchthat DMX control words may be correctly addressed to the correspondingDC-DC converter to correctly control the intensity of the associated LEDarray.

In addition, firmware loaded via USB 1012 may be used to select thetemperature trigger value, such that either fan RPM may be increased orLED array current drive may be decreased (as discussed above) once thetemperature trigger value (e.g., as detected by temperature sensors1016) is exceeded. Dim control may also be selected via firmware loadedvia USB 1012 to, for example, select the rate at which the LED array(s)may be dimmed. For example, each DMX control word (e.g., 256 controlwords per DMX slot total) may correspond to a particular LED arrayintensity as may be controlled by a corresponding PWM signal asgenerated by CPU 1018. User controllable dimming as defined by firmwareloaded via USB 1012 may, for example, be used to select the rate atwhich such intensity variation occurs.

Turning to FIG. 11, a schematic diagram of lighting system 1100 isillustrated, which may include AC/DC converter 1102 (e.g., power supply904 of FIG. 9), which may include one or more constant current and/orconstant voltage DC output stages (e.g., DC stages 1110, 1112 and/or1140) and an auxiliary low voltage output (e.g., 5 VDC not shown) withwhich components (e.g., processor 1104, wireless node 1106 and wirednode 1108 of lighting system 1100) may derive their operational power.Any one or more of DC output stages 1110, 1112 and 1140 may providepower via any one or more switched-mode conversion techniques (e.g.,buck, boost, buck/boost or flyback). Conversely, linear power conversiontechniques may also be utilized that obviate the need for switched-modeconversion and may provide low electromagnetic emissions and excellenttransient response.

AC/DC converter 1102 may be configured to provide sufficient power to,for example, vary the intensity of the one or more arrays of LEDscontained within one or more horticulture lights (e.g., one or morehorticulture lights as exemplified in FIG. 9). It should be noted thatwhile only two LED arrays 1122 and 1124 are exemplified, any number ofLED arrays 1138 and associated bias control circuitry may beaccommodated by any number of DC stages within AC/DC converter 1102.Furthermore, each LED array 1122 and 1124 may include virtually anynumber (e.g., one or more) of LEDs 1144 and 1146, respectively.

As discussed in more detail below, the magnitude of DC voltage availablefrom any one DC stage 1110, 1112 or 1140 may be adjusted as needed(e.g., via control 1148 from processor 1104) to be substantially equalto the combined forward voltage of any one associated LED string 1122,1124 or 1138. In one embodiment, for example, processor 1104 mayempirically deduce the magnitude of forward voltage required to forwardbias each LED in each string LED string 1122, 1124 and/or 1138. Once themagnitude of forward voltage needed to forward bias each LED in each LEDstring 1122, 1124 and/or 1138 is known, processor 1104 may then commandone or more associated DC stages 1110, 1112 and/or 1140 (e.g., viacontrol 1148) to the determined magnitude of forward voltage so thateach LED string may be operated as efficiently as possible. In alternateembodiments, DC stages 1110, 1112 and/or 1140 may automaticallydetermine the magnitude of forward voltage needed to forward bias eachLED in each LED string 1122, 1124 and/or 1138 and may communicate thatvoltage to processor 1104 (e.g., via control 1148).

In one embodiment, each LED array may be configured to operate inaccordance with one or more bias topologies. As per one example, LEDarray 1122 and 1124 may be configured in parallel to operate using asingle voltage rail (e.g., a single voltage rail generated by one of DCstages 1110, 1112 or 1140) such that switches 1118 and/or 1120 may beconfigured as shown (e.g., via control 1148 from processor 1104) toproduce a forward voltage across each LED array and a forward currentthrough each LED array as may be modulated by a power switch (e.g.,field effect transistors (FETs) 1150 and/or 1152) via control signals1154 and/or 1156, respectively, as may be appropriately level shifted bylevel shifters 1180 and 1182, respectively, whereby the currentconducted by each LED array may be stabilized via ballast elements(e.g., resistors 1126 and 1128). Other power switching elements, such asinsulated gate bipolar transistors (IGBTs) or vertical MOSFETs, may beused instead of FETs 1150 and 1152 as well.

As per another example, each LED array may be configured in parallel tooperate using a single voltage rail (e.g., a single voltage railgenerated by DC stage 1110 or DC stage 1112) whereby switches 1118 and1120 may be configured in the opposite configuration as shown to producea forward voltage across each LED array and a forward current througheach LED array as may be modulated by a power switch (e.g., FETs 1150and 1152) via control signals 1154 and/or 1156, respectively, as may beappropriately level shifted by level shifters 1180 and 1182,respectively, whereby the average current conducted by each LED arraymay be stabilized via a current stabilization network (e.g., inductor1130/diode 1132 and inductor 1134/diode 1136, respectively).

Still other examples include configurations whereby each LED array(e.g., LED array 1122 and 1124) may be operated independently using adedicated DC stage (e.g., DC stage 1112 and DC stage 1110, respectively)in either of a constant voltage or constant current configuration usingeither ballast or inductor-based current stabilization techniques as maybe selected by switches 1118 and 1120.

As discussed in more detail below, wired node 1108 may include any wiredinterface (e.g., DMX, I2C, Ethernet, USB, DALI, 0-10V, etc.) that may beused to configure lighting system 1100 (e.g., via processor 1104) foroperation and/or allow processor 1104 to communicate the status andoperational capability of lighting system 1100 to wired network 1158(e.g., BACnet-enabled wired network 1158). Similarly, wireless node 1106may include any wireless interface (e.g., Wi-Fi, thread-based mesh,Bluetooth, ZigBee, etc.) that may similarly be used to configurelighting system 1100 (e.g., via processor 1104) for operation and/orallow processor 1104 to communicate the status and operationalcapability of lighting system 1100 to wireless network 1160 (e.g.,BACnet-enabled wireless network 1160).

As discussed above, processor 1104 may be configured to deduce thenumber of LED strings that may be under its control as well as thenumber of LEDs in each LED string. Such deduction, for example, mayoccur each time lighting system 1100 is provisioned with LEDs, either atinitial deployment or after reconfiguration. Processor 1104 may thenconfigure the operation of AC/DC converter 1102 for optimal performancein response to the number of LED strings found and/or the number of LEDsin each LED string subsequent to such deduction. Accordingly, the numberof LED strings and the number of LEDs in each LED string containedwithin lighting system 1100 may not necessarily be fixed at initialdeployment or after each reconfiguration, but rather may be dynamic suchthat processor 1104 may intelligently determine the lighting capabilityof lighting system 1100 (e.g., the number of LED strings and the numberof LEDs in each LED string after initial deployment and/or after eachreconfiguration) and may, therefore, intelligently select the mostefficient mode of operation of each DC stage (e.g., constant current,constant voltage or a mixture of both), the most efficient magnitude ofvoltage and/or current to be generated by each DC stage and may alsointelligently select the most efficient current stabilization mode foreach LED string (e.g., ballast or inductor-based current stabilization).

It should be noted that the mode of operation of DC stages 1110, 1112and 1140 may be programmable (e.g., via control 1148 of processor 1104)to either a constant-voltage or a constant-current mode of operation.Conversely, the mode of operation of DC stages 1110, 1112 and 1140 maybe fixed such that a mixture of both constant-voltage andconstant-current DC stages may exist within AC/DC converter 1102 and maybe individually selected for operation (e.g., via control 1148 ofprocessor 1104) and individually connected to respective LED strings1122, 1124 and/or 1138 via a multiplexer (not shown) within AC/DCconverter 1102.

In alternate embodiments, each DC stage of AC/DC converter 1102 may bepaired with either a ballast-based current stabilization network or aninductor-based current stabilization network, such that switches 1118and 1120 may no longer be necessary. In addition, the operational modeof each DC stage (e.g., constant-current or constant-voltage) may bepredetermined, such that upon configuration of lighting system 1100, LEDstrings 1122, 1124 and/or 1138 may be statically paired with aballast-based current stabilization network, an inductor-based currentstabilization network, or both, and each pairing may includeconstant-voltage and/or constant-current topologies.

Turning to FIG. 12, flow diagrams are exemplified whereby processor 1104may first discover the number of LED strings initially provisionedand/or reconfigured within lighting system 1100. Next, processor 1104may then configure the bias and stabilization networks of lightingsystem 1100 that may be necessary for the most efficient mode ofoperation of each detected LED string.

In step 1202, for example, processor 1104 may first select a continuitymode, whereby AC/DC converter 1102 may be selected to perform acontinuity test to determine the number of LED strings that may existwithin lighting system 1100. Initially, a first DC stage of AC/DCconverter 1102 (e.g., DC stage 1112) may be configured by processor 1104via control 1148 to provide a maximum output voltage (e.g., 250 VDC) asin step 1204, which may then be applied to a first LED string (e.g., LEDstring 1122 in a current-limited fashion). In one embodiment, forexample, processor 1104 may select switch 1118 to the position shown viacontrol 1148 and FET 1150 may be momentarily rendered conductive byprocessor 1104 via control 1154 (e.g., as in step 1206). In response, acurrent may or may not be conducted by resistor 1126, as may be sensedby current sensor 1162 of processor 1104, to determine whether or notLED string 1122 exists within lighting system 1100. A voltage developedacross resistor 1126, for example, may lead to the determination that aparticular magnitude of current is being conducted by LED string 1122,which may then lead processor 1104 to deduce that LED string 1122 existswithin lighting system 1100. Steps 1202-1206 may then be repeated asabove (e.g., with the same DC stage or a different DC stage within AC/DCconverter 1102) to determine the number of LED strings that may or maynot exist within lighting system 1100, the result may then be logged asin step 1208.

For the one or more LED strings that may be detected through executionof steps 1202-1208 by processor 1104, a substantially minimum magnitudeof forward voltage may then be empirically determined such that each LEDstring may be operated at maximum efficiency using the determinedminimum magnitude of forward voltage. For example, processor 1104 mayfirst select a continuity mode (as in step 1210), whereby AC/DCconverter 1102 may be selected to perform a continuity test to determinethe forward voltage required to illuminate all of the LEDs that mayexist within a previously detected LED string. A first DC stage of AC/DCconverter 1102 (e.g., DC stage 1112) that may correspond to the firstdetected LED string may first be configured by processor 1104 viacontrol 1148 to provide a maximum output voltage (e.g., 250 VDC) as instep 1212, which may then be applied to the first detected LED string(e.g., LED string 1122 in a current-limited fashion) as discussed above,for example, in relation to step 1206.

In step 1214, the applied voltage may be modulated (e.g., decreased from250 VDC) by processor 1104 via control 1148 in coarse voltage steps(e.g., 10V steps) until current stops flowing (e.g., as detected bycurrent sense 1162 as the applied voltage is decreased from 250 VDC).The coarse voltage obtained in step 1214 may then be logged by processor1104 as the minimum coarse voltage magnitude required to illuminate theLED string.

In step 1216, the DC stage may be programmed to the minimum coarsevoltage from step 1214 increased by one coarse voltage step and thenmodulated (e.g., decreased) by processor 1104 via control 1148 in mediumvoltage steps (e.g., 1V steps) until current stops flowing (e.g., asdetected by current sense 1162). The medium voltage obtained in step1216 may then be logged by processor 1104 as the minimum medium voltagemagnitude required to illuminate the LED string.

In step 1218, the DC stage may be programmed to the sum of the minimumcoarse voltage from step 1214 and the minimum medium voltage from step1216 increased by one medium voltage step and then modulated (e.g.,decreased) by processor 1104 via control 1148 in fine voltage steps(e.g., 0.1V steps) until current stops flowing (e.g., as detected bycurrent sense 1162). The voltage may then be increased in fine voltagesteps (e.g., 0.1 VDC steps) until the current begins to flow again. Thefine voltage obtained in step 1218 may then be logged by processor 1104as the minimum fine voltage magnitude required to illuminate the LEDstring.

Once steps 1214-1218 have been completed, the minimum forward voltagerequired to most efficiently illuminate the LED string may have beendetermined within a minimum voltage resolution (e.g., 0.1 VDC). Forexample, if the LED string under test contains 72 LEDs where each LEDexhibits a forward voltage of 3.1 volts and assuming that theon-resistance of FET 1150 and the resistance of resistor 1126 adds anadditional overhead voltage (e.g., 0.5 VDC) to the magnitude of forwardvoltage required to illuminate LED string 1122, then a minimum forwardvoltage of approximately 72*3.1+0.5=223.7 VDC (e.g., constituting acoarse voltage magnitude of 220 VDC, a medium voltage magnitude of 3 VDCand a fine voltage magnitude of 0.7 VDC) would be required to illuminatethe LED string under test. In such an instance, the first DC stage ofAC/DC converter 1102 (e.g., DC stage 1112) corresponding to the firstdetected LED string of lighting system 1100 may be programmed byprocessor 1104 via control 1148 to provide approximately 223.7 VDC(perhaps rounding up to 225-230 volts for increased headroom), insteadof the maximum output voltage (e.g., 250 VDC), such that the firstdetected LED string of lighting system 1100 may be operated at the mostefficient voltage rail possible (e.g., substantially equal to the sum offorward voltages (V_(f)) of all LEDs in the LED string plus the FET,current sense and miscellaneous voltage overhead) and the currentmagnitude corresponding to such voltage may be measured (e.g., viacurrent sense 1162) and logged by processor 1104 (e.g., as in step1220). It should be noted that reduced resolution may be obtained whendetermining the minimum forward voltage required to most efficientlyilluminate the LED string by simply eliminating step 1218 or steps 1218and 1216.

In an alternate embodiment (e.g., as in step 1224), the applied voltagemay be modulated (e.g., increased from 0 VDC) by processor 1104 viacontrol 1148 in coarse voltage steps (e.g., 10V steps) until currentbegins to flow (e.g., as detected by current sense 1162 as the appliedvoltage is increased from 0 VDC). The coarse voltage obtained in step1224 may then be decreased by one coarse voltage step and then logged byprocessor 1104 as the minimum coarse voltage magnitude required toilluminate the LED string.

In step 1226, the DC stage may be programmed to the minimum coarsevoltage from step 1224 and then modulated (e.g., increased) by processor1104 via control 1148 in medium voltage steps (e.g., 1V steps) untilcurrent begins to flow (e.g., as detected by current sense 1162). Themedium voltage obtained in step 1226 may be decreased by one mediumvoltage step and then logged by processor 1104 as the minimum mediumvoltage magnitude required to illuminate the LED string.

In step 1228, the DC stage may be programmed to the sum of the minimumcoarse voltage from step 1224 and the minimum medium voltage from step1226 and then modulated (e.g., increased) by processor 1104 via control1148 in fine voltage steps (e.g., 0.1V steps) until current begins toflow (e.g., as detected by current sense 1162). The fine voltageobtained in step 1228 may then be logged by processor 1104 as theminimum fine voltage magnitude required to illuminate the LED string.Once steps 1224-1228 have been completed, the minimum forward voltagerequired to most efficiently illuminate the LED string may have beendetermined within a minimum voltage resolution (e.g., 0.1 VDC) similarlyas discussed above in relation to steps 1214 to 1218 and the currentmagnitude corresponding to such voltage may be measured (e.g., viacurrent sense 1162) and logged by processor 1104 (e.g., as in step1220). It should be noted that reduced resolution may be obtained whendetermining the minimum forward voltage required to most efficientlyilluminate the LED string by simply eliminating step 1228 or steps 1228and 1226.

In one embodiment, processor 1104 may determine which currentstabilization mode to utilize depending upon the results of steps1210-1220 or steps 1210-1212, steps 1224-1228 and step 1220. For examplein step 1230, processor 1104 may compare the optimal forward voltage foreach detected LED string. In step 1234, comparison of the optimalforward voltage deduced for each detected LED string may lead to adetermination that each optimal forward voltage may be approximatelyequal and in such an instance, a ballast-based stabilization techniquemay be selected as in step 1236, whereby each LED string may be operatedfrom the same DC stage of AC/DC converter 1102 and the current in eachLED string may be appropriately stabilized by its associated ballastresistor and modulated (e.g., increased or decreased on average overtime) by analog control and/or appropriate control of the duty cycle ofeach power switch associated with each LED string (e.g., FET 1150/dutycycle control 1154 for LED string 1122 and FET 1152/duty cycle control1156 for LED string 1124).

If, on the other hand, the deduced optimal forward voltages for eachdetected LED string are not substantially equal, inductor-based currentstabilization may instead be selected (e.g., as in step 1238), wherebyeach LED string may be operated from independent DC stages of AC/DCconverter 1102 (e.g., constant current DC stages each set at the optimalforward voltage associated with each LED string) and the current in eachLED string may be appropriately stabilized by its associatedinductor/diode pair and modulated (e.g., increased or decreased onaverage over time) by analog control and/or appropriate control of theduty cycle of each power switch associated with each LED string (e.g.,FET 1150/duty cycle control 1154 for LED string 1122 and FET 1152/dutycycle control 1156 for LED string 1124).

It should be noted that the inductor (e.g., inductor 1130 or inductor1134) of an inductor-based current stabilization network may add anadditional forward voltage component to the minimum voltage required tooperate an LED string. However, since the voltage magnitude of each DCstage of AC/DC converter 1102 may be optimally controlled (e.g.,minimized), the magnitude of inductance required by each inductor may beminimized as well (thereby minimizing the physical size of theinductor), since the required inductance magnitude is directlyproportional to the voltage developed across the inductor.

In one embodiment, a capacitor (e.g., capacitor 1168 and 1170) may beoptionally placed across LED strings 1122 and 1124, respectively, to areference potential (e.g., ground) in either of a ballast-based orinductor-based current stabilization mode of operation. In aballast-based mode of operation, for example, the capacitor may beselected for a specific output voltage ripple to maintain asubstantially constant output voltage under load transient conditions.

In an inductor-based current stabilization mode of operation, on theother hand, capacitors (e.g., capacitors 1168 and 1170) may interactwith inductors (e.g., inductors 1130 and 1134, respectively) to provideAC current filtering, thereby allowing the capacitor to control theripple current to acceptable levels as required by each LED string whileat the same time decreasing the required inductance magnitude, therebyfurther minimizing the physical size and cost of the inductor. Forexample, by allowing smaller inductance magnitudes to be selected, theresulting increase in peak-to-peak current ripple may be conducted byeach capacitor (e.g., capacitor 1168 and 1170), thereby maintaining themagnitude of current ripple experienced by each LED string (e.g., LEDstring 1122 and 1124, respectively) to within acceptable limits (e.g.,10% of the DC forward current conducted by each LED string).

It should also be noted that other algorithms may be used to determinethe current stabilization technique other than those algorithms depictedin steps 1230-1238. For example, inductor-based current stabilizationmay be selected by processor 1104 even though the optimal forwardvoltage for each detected LED string may be approximately equal andoperated from the same or different DC stages of AC/DC converter 1102.Conversely, ballast-based current stabilization may be selected byprocessor 1104 even though the optimal forward voltage for each detectedLED string may be substantially unequal and operated from the same ordifferent DC stages of AC/DC converter 1102.

Algorithms defining the operation of lighting system 1100 (e.g.,algorithms described by the execution steps of FIG. 12) may, forexample, fully reside within processor 1104 (e.g., flash memory that islocal to processor 1104). Alternately, such algorithms may fully residewithin a network (e.g., wired network 1158 and/or wireless network 1160)whereby execution instructions associated with such algorithms may bereceived by processor 1104 via wired node 1108 and/or wireless node1106. Conversely, algorithms defining the operation of lighting system1100 (e.g., algorithms described by the execution steps of FIG. 12) maybe distributed to partially reside within processor 1104 and partiallyreside within a network (e.g., wired network 1158 and/or wirelessnetwork 1160) whereby a portion of execution instructions may bereceived by processor 1104 via wired node 1108 and/or wireless node1106.

In operation, the status of lighting system 1100 may be continuouslymonitored and such status may be relayed to wired network 1158 and/orwireless network 1160 via wired node 1108 and/or wireless node 1106,respectively. As per one example, processor 1104 may continuouslymonitor the current conducted by each LED string (e.g., LED strings1122, 1124 and/or 1138 as may be measured by current sense 1162, 1164and/or 1166, respectively) to determine whether each LED string isoperating in accordance with the logged current magnitudes for each LEDstring (e.g., as logged by step 1220 of FIG. 12). A detected fault(e.g., zero conducted current) in one LED string, for example, mayresult in the deactivation of at least the faulted LED string andperhaps the remaining LED strings by causing the associated voltage andcurrent regulation devices (e.g., FETs 1150 and/or 1152) to remainnon-conductive (e.g., via control signals 1154 and 1156, respectively).Such detected faults and subsequent actions taken by processor 1104 maythen be reported (e.g., via wired network 1158 and/or wireless network1160) to allow maintenance personnel to react to the reported fault(e.g., decommissioning of the faulted lighting system and the subsequentcommissioning of a replacement lighting system).

In alternate embodiments, trends of each LED string may be tracked topredict, for example, efficiency, maximum light output, peak wavelengthand spectral wavelength variations due to increased junctiontemperature. Increased junction temperatures, for example, may berelated to a forward voltage decrease of a particular LED string due toa reduction in the bandgap energy of the active region of each LED inthe LED string as well as a decrease in the series resistance of eachLED occurring at high temperatures. Accordingly, for example, bytracking a reduced forward voltage of a particular LED string over time,predictions may be made and reported by processor 1104 (e.g., via wirednetwork 1158 and/or wireless network 1160) as to certain performanceparameters of each LED string so that maintenance personnel may respondaccordingly.

Turning to FIG. 13, an alternate embodiment of lighting system 1300 isexemplified, such that the current stabilization topologies may not beselectable and may instead be provided as ballast-based currentstabilization networks for each LED string utilized within lightingsystem 1300 or not at all. For example, the forward voltage (V_(f)) ofeach LED string 1322, 1380 and 1324 may be closely matched such thatballast elements 1326, 1382 and 1328, respectively, may not benecessary. In addition, a single DC stage 1340 may be utilized withinAC/DC converter 1302, which may provide a single-rail voltage magnitude(e.g., via voltage signal 1390 at node 1310) in a constant-current modeof operation to multiple LED strings connected in a parallelconfiguration (e.g., LED strings 1322, 1324 and 1380).

Similarly as discussed above in relation to FIG. 11, wired node 1308 mayinclude any wired interface (e.g., DMX, I2C, Ethernet, USB, DALI, 0-10V,etc.) that may be used to configure lighting system 1300 (e.g., viaprocessor 1304) for operation and/or allow processor 1304 to communicatethe status and operational capability of lighting system 1300 to wirednetwork 1358 (e.g., BACnet-enabled wired network 1358). Similarly,wireless node 1306 may include any wireless interface (e.g., Wi-Fi,thread-based mesh, Bluetooth, ZigBee, etc.) that may similarly be usedto configure lighting system 1300 (e.g., via processor 1304) foroperation and/or allow processor 1304 to communicate the status andoperational capability of lighting system 1300 to wireless network 1360(e.g., BACnet-enabled wireless network 1360).

The number of series-connected LEDs (e.g., one or more) in each LEDstring (e.g., 1322, 1324 and 1380) may be selected based upon the sum offorward voltage (V_(f)) of each series-connected LED, where the forwardvoltage of each LED string may be selected to be substantially equal. Inone embodiment, for example, an LED string may be selected to containabout 45 to 50 (e.g., 46) LEDs each having a V_(f) between about 2.5Vand 3.5V (e.g., 3V) for a cumulative forward voltage of 46*3=138V forthe LED string. In an alternate embodiment, for example, an LED stringmay be selected to contain about 60 to 75 (e.g., 69) LEDs each having aV_(f) between about 1.5V and 2.5V (e.g., 2V) for a cumulative forwardvoltage of 69*2=138V for the LED string.

In alternate embodiments, each LED string may have the same or adifferent number of LEDs, but due to differences in V_(f) for each LEDtype in each LED string, each LED string may exhibit a forward voltagethat is substantially equal to the forward voltage of each of the otherLED strings. Furthermore, while only three LED strings are depicted, anynumber of LED strings (e.g., 4) may be utilized. Still further, each ofLED strings 1322, 1324 and 1380 may reside within a single lightingfixture or may reside within multiple lighting fixtures.

Due to slight deviations in the V_(f) for each LED of each LED string(e.g., due to forward current deviations in each LED string), thecumulative forward voltage for each LED string may not necessarilyconform to the calculations above, which may necessitate the existenceof ballast elements (e.g., resistor 1326, 1328 and 1382) such that thevoltage magnitude at node 1310 may be allowed to remain substantiallyequal under all load conditions for each LED string. Furthermore, eachballast element may facilitate current stabilization as well as currentsense measurements by processor 1304 as discussed in more detail below.

Turning to FIG. 13A, a variation of FIG. 13 is exemplified, which issimplified for clarity and ease of description. As discussed above inrelation to FIG. 13, the lighting system of FIG. 13A may provide asingle power supply (e.g., via voltage rail 1301) that may be operatingin a constant current mode of operation, such that the current conductedby LED strings 1303, 1305 and 1307 may be shared and may be controlledvia power switches 1311, 1313 and 1315, respectively, as discussedherein by processor 1309 via control signals 1317, 1319 and 1321,respectively.

LED string 1307 may, for example, represent one or more strings ofseries-connected broad spectrum white LEDs (e.g., a string ofseries-connected warm white LEDs and a string of series-connected coolwhite LEDs) that may be connected in parallel with LED string 1303(e.g., a series-connected string of deep red LEDs) and LED string 1305(e.g., a series-connected string of far red LEDs). As such, spectrumtuning may be performed by processor 1309 through adjustment of anaverage magnitude of current conducted over time by power switches 1311,1313 and 1315, respectively, thereby controlling an average intensity oflight generated over time by each LED string 1303, 1305 and 1307,respectively, as discussed herein.

Turning to FIG. 13B, a typical I-V characteristic curve is exemplified,including V_(f) magnitude 1355 that may represent, for example, theminimum V_(f) required to forward bias a particular LED (e.g., a redLED) into its conductive region (e.g., region 1351). Similarly, V_(f)magnitude 1357 may represent, for example, the minimum V_(f) required toforward bias a particular LED (e.g., a white LED) into its conductiveregion (e.g., region 1353). As illustrated, it can be seen that a V_(f)magnitude (e.g., V_(f) magnitude 1357) that may be required to forwardbias a white LED may be several multiples (e.g., a multiple of threetimes) the V_(f) magnitude (e.g., V_(f) magnitude 1355) that may berequired to forward bias a red LED. Furthermore, a substantial disparitymay exist in the forward voltage exhibited by a conductive red LED(e.g., as illustrated by the slope of the I-V curve in conductive region1351) as compared to the forward voltage exhibited by a conductive whiteLED (e.g., as illustrated by the slope of the I-V curve in conductiveregion 1353) relative to a respective change in forward current, I_(F).

As discussed above, a number of LEDs in each LED string 1303, 1305 and1307 may be selected such that the cumulative V_(f) magnitude of aseries-connected LED string (e.g., LED string 1303) may be substantiallyequal to the cumulative V_(f) magnitude of each series-connected LEDstring that may be connected in parallel to the first LED string (e.g.,LED strings 1305 and 1307). For example, the cumulative V_(f) magnitudeof series-connected LED strings 1303, 1305 and 1307 may be selected tobe substantially equal through appropriate selection of the number ofLEDs that may exist in series-connected LED strings 1303, 1305 and 1307multiplied by the V_(f) of each respective LED in each LED string. Inone embodiment according to the I-V characteristics of FIG. 13B, forexample, it can be seen that a number of LEDs (e.g., a number of far redLEDs existing in LED string 1303) and a number of LEDs (e.g., a numberof deep red LEDs existing in LED string 1305) may be selected to beapproximately three times a number of LEDs (e.g., a number of white LEDsexisting in LED string 1307) that may be necessary in order tosubstantially match the cumulative V_(f) magnitude of each of LEDstrings 1303 and 1305 to the cumulative V_(f) magnitude of LED string1307 due to the disparity in V_(f) of a white LED as compared to theV_(f) of a red LED as discussed above.

In one embodiment, however, supplying three times the number of red LEDsas compared to a number of white LEDs supplied in a particular lightingsystem may not conform to a requisite spectrum required of the lightingsystem, since in that instance, the lighting system may be overly biasedtoward the red spectrum. Accordingly, one or more LEDs that may exhibitan increased magnitude V_(f) (e.g., white LEDs 1327), for example, maybe interspersed within each of LED strings 1303 and 1305 such that therequisite cumulative V_(f) magnitude of LED strings 1303 and 1305 may beobtained without unnecessarily increasing a number of red LEDs requiredin each of LED strings 1303 and 1305. In one embodiment, for example,for each white LED that may be interspersed within each of LED strings1303 and 1305, a number (e.g., 3) red LEDs (not shown) may be displacedfrom LED strings 1303 and 1305 due to the disparity in the V_(f)magnitude of a white LED as compared to the V_(f) magnitude of a redLED.

In one embodiment, however, certain light recipes may require a limitedcolor spectrum (e.g., limited to only the far red and deep red spectrum)to be emitted by the lighting system while excluding all other spectrums(e.g., broad spectrum white). In such an instance, for example, one ormore shunt devices 1329 may be disposed (e.g., arranged in parallel)with one or more LEDs (e.g., one or more white LEDs 1327) and may beactivated (e.g., by processor via one or more shunt control signals1323) to selectively reduce the forward voltage applied across the oneor more LEDs 1327 to a voltage magnitude that may be less than theminimum voltage required to forward bias the one or more LEDs 1327 whilesimultaneously conducting the current present within the respective LEDstring (e.g., LED strings 1303 and 1305). In such an instance, shuntdevices 1329 may conduct a magnitude of current that would ordinarily beconducted by LEDs 1327 and thereby may be precluded from emitting lightwhile the remainder of LEDs in each respective LED string (e.g., redLEDs in LED strings 1303 and 1305 not shown) may be allowed to emit alight intensity in accordance with the magnitude of current conductedwithin each respective LED string (e.g., LED strings 1303 and 1305).

The one or more shunt control signals 1323 may, for example, beimplemented as a PWM signal by processor 1309 so as to control theconductive state of each shunt device 1329 (and conversely thenon-conductive state of the one or more associated LEDs 1327 connectedin parallel to each shunt device 1329) in proportion to the duty cycleof the PWM signal. Such a control mechanism may be necessary, forexample, due to the disparity in the slope of conductive region 1353 ascompared to the slope of conductive region 1351 as exemplified in FIG.13B. In particular, it can be seen from FIG. 13B that the change inforward voltage relative to the current conducted by the LED (e.g., ared LED) in region 1351 varies much more rapidly than the change inforward voltage relative to the current conducted by the LED (e.g., awhite LED) in region 1353. Accordingly, a dynamic variation in the oneor more shunt control signals 1323 (e.g., as may be provided by PWMcontrol) may be used to dynamically account for the disparity in forwardvoltage of a red LED as compared to a white LED for a given range inforward current magnitude conducted by each.

As per one example, a current magnitude conducted by LED string 1303 maybe selected to provide an intensity magnitude of far red spectrum viaprocessor 1309 according to a specified light recipe (e.g., as may bestored locally within processor 1309). However, since white LEDs 1327may exist within LED string 1303, a portion of broad white spectrumlight may also be emitted by LED string 1303, which may exceed the broadwhite spectrum intensity by a certain percentage as may be specified bythe light recipe. In such an instance, processor 1309 may select one ormore shunt control signals 1323 (e.g., a PWM shunt control signal) toremove that certain percentage of broad white spectrum by activatingshunt devices 1329 that may be associated with broad white LEDs 1327.Accordingly, one or more shunt control signals 1323 may activate shuntdevices 1329 to conduct a specified magnitude of current away from whiteLEDs 1327 to reduce the intensity of light generated by the white LEDs1327 by that certain percentage.

As per another example, LED strings 1303, 1305 and 1307 may each beconducting a specified magnitude of current that may be required by acertain light recipe (e.g., a light recipe locally stored withinprocessor 1309) to emit a specific light intensity to produce a specificCCT. As the light emitted by lighting system 1400 may be commanded to bedimmed (e.g., as wirelessly commanded by a user of lighting system 1400via wireless network 1360 of FIG. 13), a magnitude of current conductedby each of LED strings 1303, 1305 and 1307 may be reduced accordingly(e.g., by processor 1309 via appropriate control signals 1317, 1319, and1321 as discussed herein). Due to the slope disparity of I-Vcharacteristic curves 1351 and 1353, however, the cumulative forwardvoltage of LED strings 1303 and 1305 (e.g., red LED strings) may dropfaster than the cumulative forward voltage of LED string 1307 (e.g., abroad white LED string) as the current magnitude conducted by each ofLED strings 1303, 1305 and 1307 is reduced. In such an instance, shuntdevices 1329 may behave as voltage-controlled variable resistors (e.g.,via a variable R_(DS-ON) Of each respective shunt device 1329) as may becontrolled via one or more shunt control signals 1323 in conjunctionwith level shift devices 1325. In such an instance, for example, avoltage drop across each shunt device 1329 may be controlled viaprocessor 1309 by selecting an appropriate R_(DS-ON) relative to thecurrent conducted by shunt devices 1329 in order to counteract thedisparity in the slope of I-V characteristic curves 1351 and 1353 byadjusting the cumulative V_(f) of each LED string 1303 and 1305 throughadjustment of a variable voltage drop across the drain/source terminalsof each shunt device 1329.

It should be noted that level shift devices 1325 may operate as floatingshunt devices (e.g., not referenced to ground potential 1331) so as toallow proper operation irrespective of a location of the one or moreshunt devices 1329 along LED strings 1303 and 1305. Alternatively, forexample, one or more level shift devices 1325 may be decoupled fromground potential 1331 through the use of optically-coupled drivers.

Turning back to FIG. 13, processor 1304 may be configured to deduce thenumber of LED strings that may be under its control as well as theforward current requirements (e.g., minimum and maximum forward current)in each LED string. Such deduction, for example, may occur each timelighting system 1300 is provisioned with LEDs, either at initialdeployment or after reconfiguration.

Turning to FIG. 14, flow diagrams are exemplified whereby processor 1304may first discover the number of LED strings initially provisionedand/or reconfigured within lighting system 1300. Next, processor 1304may then configure the current provisioning for each LED string oflighting system 1300.

In a first embodiment, processor 1304 may have control of both thevoltage and current magnitude output of DC stage 1340 via control 1348.In such an instance, processor 1304 may configure DC stage 1340 to itsminimum voltage output (e.g., as in step 1402) and its maximum currentoutput (e.g., as in step 1404). Processor 1304 may then configurelighting system 1300 for a continuity check (e.g., as in step 1406)whereby, for example, processor 1304 may render one of LED strings 1322,1380 and 1324 conductive by transitioning one of power switches (e.g.,FETs 1350, 1352 or 1386, respectively), into a conductive state. In step1408, the output voltage magnitude of DC stage 1340 may be increased(e.g., as in steps 1224 through 1228 of FIG. 12) until current isconducted through the LED string under test (e.g., as may be detected bycurrent sense 1362, 1366 or 1364, respectively). Processor 1304 may thendecrease the current conducted by the LED string under test via control1348 by programming the current output of DC stage 1340 to decreasinglylower magnitudes (e.g., in 1 mA steps decreasing from the maximumcurrent set in step 1404) until current ceases to flow (e.g., as in step1410). In step 1412, for example, processor 1304 may then log theminimum voltage and current magnitudes as measured by steps 1408 and1410 into a memory location (e.g., as located on-board processor 1304and/or as may be located in memory locations of wired network 1358and/or wireless network 1360).

In an alternate embodiment, processor 1304 may program the currentmagnitude output of DC stage 1340 via control 1348, but DC stage 1340may internally adjust the output voltage as required to produce theprogrammed current magnitude output of DC stage 1348. In such aninstance, processor 1304 may configure DC stage 1340 to its maximumcurrent output (e.g., as in step 1414). Processor 1304 may thenconfigure lighting system 1300 for a continuity check (e.g., as in step1416) whereby, for example, processor 1304 may render one of LED strings1322, 1380 and 1324 conductive by transitioning one of power switches(e.g., FETs 1350, 1352 or 1386, respectively), into a conductive state.The output voltage magnitude of DC stage 1340 may then be internallyincreased (e.g., increased by circuitry located internal to DC stage1340) until current is conducted through the LED string under test(e.g., as may be detected by current sense 1362, 1366 or 1364,respectively). Processor 1304 may then decrease the current conducted bythe LED string under test via control 1348 by programming the currentoutput of DC stage 1340 to decreasingly lower magnitudes (e.g., in 1 mAsteps decreasing from the maximum current set in step 1414) untilcurrent ceases to flow (e.g., as in step 1418). In step 1420, forexample, processor 1304 may then log the minimum voltage (e.g., as maybe reported by DC stage 1340 to processor 1304 via control 1348) andcurrent magnitudes (e.g., minimum and maximum current magnitudes) asmeasured by step 1418 into a memory location (e.g., local to processor1304 and/or as may be located in memory locations of wired network 1358and/or wireless network 1360).

Once the initial configuration of each LED string is complete andlighting system 1300 is operational, each subsystem of lighting system1300 may be monitored (e.g., as in step 1422) to, for example,continuously determine the operational status of lighting system 1300.For example, each LED string of lighting system confirmed to beoperational (e.g., as in steps 1402-1412 or steps 1414-1420) may becontinuously monitored (e.g., the forward current of each LED string maybe continuously monitored) for normal operation. If the measured forwardcurrent substantially equals the current magnitudes as logged in steps1412 or 1420 taking into account any digital current modulationperformed by power switches (e.g., FETs 1350, 1352 and/or 1386), such asreduced forward current through less than 100% duty cycle modulation ofthe power switches, then normal status of lighting system 1300 may bereported (e.g., as in step 1426). If, on the other hand, the modulatedforward current does not meet previously verified current magnitudes,then abnormal status of lighting system 1300 may be reported (e.g., asin step 1428) and reported to, for example, wired network 1358 and/orwireless network 1360 to alert maintenance personnel of the abnormalstatus.

Other operational aspects of lighting system 1300 may be monitored aswell. For example, temperature sensors and fans (e.g., temperaturesensors 1016 and fans 1014 as exemplified in FIG. 10) may be utilized bylighting system 1300 to ensure that, for example, the temperature ofeach LED string is operating within specification. If not, the abnormaltemperature and/or fan malfunction may be reported as in step 1428;otherwise, normal fan and temperature status may be reported as in step1426.

Processor 1304 may implement a hybrid dimming scheme, whereby bothdigital modulation of LED string current (e.g., via PWM control of thepower switches) and analog modulation of LED string bias current may beused to provide deep dimming control of the LED string intensity whileminimizing audible and radiated noise. In step 1430, for example, theminimum and maximum current magnitudes (e.g., as determined in steps1414 and 1418) may be accessed by processor 1304 to determine the fullrange of DC bias current magnitudes (e.g., as produced by DC stage 1340)that may be utilized to illuminate a particular LED string (e.g., LEDstring 1322) across a range of intensity. As per one example, themaximum current for an LED string (e.g., LED string 1322) may bedetermined to be equal to an upper current limit (e.g., 1.25 A asdetermined in step 1414 so that LED string 1322 may produce fullintensity), whereas the minimum current for the LED string may bedetermined to be equal to a percentage of the upper current limit (e.g.,30% of 1.25 A or 0.375 A).

In step 1432, processor 1304 may determine the range over which analogcontrol of the current magnitude may be used to select a particularintensity of light emission from a particular LED string. In oneembodiment, for example, processor 1304 may determine that for allcurrent magnitudes conducted by an LED string (e.g., LED string 1322)between a maximum current magnitude and a minimum threshold currentmagnitude (e.g., 30% of the maximum current magnitude), analog control(e.g., the continuous bias current magnitude provided by DC stage 1340as commanded by control 1348) may be used. That is to say for example,that for light intensities produced by LED string 1322 between a maximumintensity and a lower threshold intensity (e.g., 30% of maximumintensity), processor 1304 may command DC stage 1340 to the desired biascurrent magnitude via control 1348 as required to produce the desiredintensity range (e.g., 1.25 A of continuous DC bias current for maximumintensity and 0.375 A of continuous DC bias current for 30% intensity).Variation between maximum intensity and the lower threshold intensitymay be accomplished through variation of the continuous DC bias currentgenerated by DC stage 1340 via control 1348 from processor 1304 inprogrammable steps (e.g., 1 mA steps). In each instance, the averagedcurrent conducted by LED string 1322 may be equal to the continuous DCbias current generated by DC stage 1340 as delivered to LED string 1322via node 1310, as may be controlled by FET 1350 in accordance with anappropriate DC control signal 1354 applied to the gate terminal of FET1350.

In step 1434, processor 1304 may determine the range over which digitalcontrol of the current magnitude may be used to select a particularintensity (e.g., below the lower threshold intensity) of light emissionfrom a particular LED string. In one embodiment, for example, processor1304 may determine that for all current magnitudes conducted by an LEDstring (e.g., LED string 1322) between the lower threshold intensity(e.g., 30% of maximum intensity) and a minimum intensity (e.g., 1% ofmaximum intensity), digital control (e.g., PWM modulation of FET 1350 toproduce a discontinuous current signal where the current signal isreduced from a non-zero magnitude to a zero magnitude according to theduty cycle of the PWM modulation over multiple periods) may be used. Inparticular, any number (e.g., 256) of PWM duty cycle variations may beused to modulate the minimum bias current generated by DC stage 1340 andprovided to LED string 1322 via node 1310 between an average biascurrent (e.g., averaged over multiple periods of maximum duty cyclediscontinuities in the current signal) required to produce the lowerthreshold intensity and an average bias current (e.g., averaged overmultiple periods of minimum duty cycle discontinuities in the currentsignal) required to produce the minimum intensity.

In step 1436, dimming may be adjusted through a combination of bothanalog and digital controls. As per one example, analog control of lightintensities produced by an LED string (e.g., LED string 1322) between amaximum intensity and a lower threshold intensity (e.g., 30% of maximumintensity) may be accomplished via appropriate control of DC stage 1340via control 1348 to generate continuous DC bias current magnitudesrequired to produce intensities between the maximum intensity (e.g.,1.25 A bias current magnitude) and the lower threshold intensity (e.g.,0.375 A bias current magnitude) in programmable and continuous currentsteps (e.g., 1 mA steps) for an intensity control granularitysubstantially equal to, for example, (0.001/(1.25−0.375))*100≅0.1%. Asper the same example, digital control of light intensities produced byan LED string (e.g., LED string 1322) between the lower thresholdintensity (e.g., 30% of maximum intensity) and a minimum intensity(e.g., 1% of maximum intensity) may be accomplished via appropriatemodulation of the lower threshold bias current generated by DC stage1340 via PWM control 1354 to produce discontinuities in the bias currentto program light intensities below the lower threshold intensity. In oneembodiment, for example, 256 DMX control values via wired node 1308 maybe used to vary the intensity between the lower threshold intensity(e.g., 30% of maximum intensity using maximum duty cycle discontinuitiesin the bias current) and the minimum intensity (e.g., 1% of maximumintensity using minimum duty cycle discontinuities in the bias current)with a control granularity substantially equal to (30%−1%)/256≅0.1%.

Through implementation of PWM control only over the lower portion of thecurrent control range (e.g., the lower 30% of the current controlrange), fidelity may be improved within that range by, for example,reducing conducted emissions, reducing radiated emissions and reducingaudible noise pollution. Furthermore, color mixing control across allLED strings (e.g., LED strings 1322, 1380 and 1324) may be enhancedthrough the application of digital dimming control beyond thelimitations conventionally imposed by analog dimming, which for example,may deteriorate when analog dimming is attempted below a thresholddimming percentage (e.g., 10% of maximum intensity). Furthermore, bylimiting the digital dimming control to lower levels of intensity (e.g.,1% to 30% of maximum intensity), the frequency of discontinuities in thePWM control waveform may be increased to frequencies above about 20 kHz(e.g., between about 20 kHz and 1 MHz) that may be less prone togenerate detectable flicker and shimmer thereby further enhancingdimming fidelity.

In one embodiment, processor 1304 may determine that DC stage 1340 maynot provide a magnitude of current that may be required by each of LEDstrings 1322, 1324 and 1380 operating at 100% intensity or lower. Insuch an instance, processor 1304 may implement a current sharingalgorithm whereby each of the LED strings 1322, 1380 and 1324 may beoperated at a percentage intensity that may be accommodated by DC stage1340. For example, DC stage 1340 may only be capable of providing anupper limit of current magnitude (e.g., 1.2 A) and in such and instance,processor 1304 may apportion a percentage of the upper limit currentmagnitude to each of LED strings 1322, 1380 and 1324 as may be necessaryusing analog control, digital control or a combination of analog anddigital control as discussed above.

It should be noted that any one LED string may be apportioned 100% ofthe available current from DC stage 1340 using the current sharingalgorithm. Conversely, any number of LED strings may share any portionof the available current from DC stage 1340. As per one example, eachLED string may equally share in the available current, whereby themagnitude of current apportioned to any one LED string may be calculatedas the maximum current available divided by the number of activated LEDstrings (e.g., three activated LED strings may each receive 0.4 A of theavailable 1.2 A from DC stage 1340) by any of an analog, digital orcombination of analog/digital current control algorithm as discussedabove.

In an alternate embodiment, for example, processor 1304 may determinethat DC stage 1340 may provide a magnitude of current that may meet orexceed the requirement of any one or more LED strings 1322, 1324 and1380 operating at 100% intensity or lower. In such an instance,processor 1304 may implement a current provisioning algorithm wherebyany one or more of the LED strings 1322, 1380 and 1324 may be operatedat a commanded percentage intensity using a combination of analog and/ordigital current control as discussed above.

As per one example, DC stage 1340 may be commanded to a currentmagnitude of 1.2 A, but each of LED strings 1322, 1380 and 1324 may onlyrequire 0.4 A on average via appropriate PWM control of their associatedpower switches (e.g., FETs 1350, 1352 and 1386, respectively) to operateat their respective commanded intensity. In such an instance, 1.2 A maybe conducted instantaneously by any one LED string 1322, 1380 and 1324at a time (e.g., only one of LED strings 1322, 1380 and 1324 may beconductive at any given time), but through time division multiple access(TDMA) control, each LED string may be operating at 33% duty cycle toreceive only the required 0.4 A on average to operate at its commandedintensity. It should be noted that through analog and/or digital currentcontrol and proper time division multiple access to such controlledcurrent, any one LED string may operate at any intensity (e.g., 0-100%)at any given time (e.g., any one LED string may be conductive to themutual exclusion of all of the other LED string conductivity states) tooperate on average at the commanded intensity.

Examples of such TDMA control are illustrated in FIGS. 15A, 15B, 15C,15D and 15E. In FIG. 15A, for example, in any given TDMA period 1502,any LED string (e.g., any of LED strings 1322, 1380 and/or 1324 of FIG.13) may be allocated a time slot (e.g., time slots 1504, 1506 and 1508,respectively) within which any one LED string may receive any magnitudepercentage (e.g., 0-100%) of any of an analog and/or a digitallycontrolled current signal (e.g., current signals 1392, 1394 and 1396 ofFIG. 13, respectively).

In time slot 1504, for example, processor 1304 may command LED string1322 to conduct a percentage (e.g., 100%) of the maximum availablecurrent by causing a maximum magnitude of bias current from acorresponding DC stage (e.g., DC stage 1340 via control 1348) to beconducted by LED string 1322. Capacitor 1368 may, for example, beutilized to extend the on-time of LED string 1322 by allowing thecurrent conducted at the end of time slot 1504 to decay into thebeginning of time slot 1506 in accordance with the RC time constantcreated by capacitor 1368 in combination with the resistance of each LEDin LED string 1322. In such an instance, for example, the light emittedby LED string 1322 at the end of time slot 1504 may be blended with thelight emitted by LED string 1380 at the beginning of time slot 1506 soas to implement true mixing of the light emitted by LED string 1322 withthe light emitted by LED string 1380 across the end of time slot 1504and into the beginning of time slot 1506.

In time slots 1506 and 1508, LED strings 1380 and 1324, respectively,may similarly be programmed to receive analog and/or digitallycontrolled current signals so that a percentage (e.g., 100%) of themaximum available current from DC stage 1340 may be received by each ofLED strings 1380 and 1324 in their respective time slots. Capacitors1372 and 1370 may, for example, be similarly utilized to extend theon-time of LED strings 1380 and 1324, respectively, by allowing thecurrent conducted at the end of time slot 1506 to decay into thebeginning of time slot 1508 and by allowing the current conducted at theend of time slot 1508 to decay into the beginning of time slot 1504 inaccordance with the RC time constants created by capacitors 1372 and1370, respectively, in combination with the resistance of each LED inLED strings 1380 and 1324, respectively. In such an instance, forexample, the light emitted by LED string 1380 at the end of time slot1506 may be blended with the light emitted by LED string 1324 at thebeginning of time slot 1508 and the light emitted by LED string 1324 atthe end of time slot 1508 may be blended with the light emitted by LEDstring 1322 at the beginning of time slot 1504.

In alternate embodiments, capacitors 1368, 1372 and 1370 may not existat all and optional slew rate control 1393, 1395 and 1397 may instead beimplemented either as hardware networks or executed in software byprocessor 1304. Slew rate control 1393, 1395 and 1397 may, for example,be implemented via hardware and may include resistor/capacitor networkscombined with other elements (e.g., diodes) to increase or decrease theslew rate of control signals 1354, 1342 and 1356, respectively, therebycontrolling the rate at which power switches 1350, 1352 and 1386,respectively, become conductive and/or non-conductive. Slew rate control1393, 1395 and 1397 may, for example, be implemented via software,whereby processor 1304 may execute embedded firmware or commands issuedby wired network 1358 or wireless network 1360 to increase or decreasethe slew rate of control signals 1354, 1342 and 1356, respectively,thereby controlling the rate at which power switches 1350, 1352 and1386, respectively, become conductive and/or non-conductive.

It should be noted that since each of LED strings 1322, 1380 and 1324may receive a maximum bias current magnitude in each of respective timeslots 1504, 1506 and 1508 and since each of time slots 1504, 1506 and1508 are of equal time duration, the average amount of current conductedby each of LED strings 1322, 1380 and 1324 over multiple time periods1502 is substantially equal to about ⅓ the maximum current availablefrom DC stage 1340.

Stated differently, the average magnitude of current conducted by anyone of LED strings 1322, 1380 or 1324 over multiple periods 1502 may becalculated by multiplying the current available from DC stage 1340(e.g., as selected by control 1348) by the ratio of time slot 1504, 1506or 1508, respectively, to period 1502, which as stated above may beequal to ⅓ since each time slot exhibits an equal time duration.

It should be further noted that current conducted by LED strings 1322,1380 and 1324 in each of time slots 1504, 1506 and 1508, respectively,may be modulated (e.g., pulse width modulated) to further reduce theaverage amount of current conducted over time. As discussed above, forexample, any one of 256 duty cycle selections may be made by processor1304 such that the amount of current conducted by each LED string 1322,1380 and 1324 in each time slot 1504, 1506 and 1508, respectively, maybe further reduced on average by the duty cycle selection of controlsignals 1354, 1342 and 1356, respectively.

FIG. 15A exemplifies a TDMA current sharing mode whereby each of LEDstrings 1322, 1380 and 1324 may share a magnitude of current (e.g.,0-100% of the current available from DC stage 1340 as selected byprocessor 1304 via control 1348) during each of mutually exclusive timeslots 1504-1508. If the time duration of time slots 1504-1508 aresubstantially equal during time period 1502, then as discussed above forexample, the average current magnitude conducted by each of LED strings1322, 1380 and 1324 over multiple time periods 1502 may be substantiallyequal to ⅓ the magnitude of current provided by DC stage 1340 onaverage. Stated differently, each of LED strings 1322, 1380 and 1324 mayconduct all of the current provided by DC stage 1340 during respectivemutually exclusive time slots 1504-1508, but since each time slotconstitutes an amount of time substantially equal to ⅓ of time period1502, then on average, each of LED strings 1322, 1380 and 1324 mayconduct a magnitude of current over multiple time periods 1502 that maybe substantially equal to ⅓ the magnitude of current provided by DCstage 1340.

TDMA current sharing mode, however, may rely upon each LED stringassociated with each TDMA time slot to conduct the entire magnitude ofcurrent provided by DC stage 1340. Accordingly, each LED of each LEDstring may be operating at a reduced efficacy (e.g., as measured inlumens per watt), since LED efficacy may be inversely proportional tothe magnitude of current conducted by each LED. In order to increase theefficacy of each LED of each LED string while conducting the same amountof current on average, for example, processor 1304 may transition from aTDMA current sharing mode to a direct drive mode, whereby each LEDstring (e.g., LED strings 1322, 1380 and 1324) may continuously conducta reduced magnitude of current during the entire period 1502 that may besubstantially equal to the averaged amount of current conducted by eachLED string while operating in a TDMA current sharing mode.

As discussed above, for example, FIG. 15A exemplifies a TDMA currentsharing mode whereby each LED string 1322, 1380 and 1324 may conduct allof the current provided by DC stage 1340, but since each TDMA time slotis substantially equal to ⅓ of time period 1502, the current magnitudeconducted on average over multiple time periods 1502 may besubstantially equal to ⅓ the current provided by DC stage 1340. In thisinstance and in order to increase LED efficacy, for example, processor1304 may transition to a direct drive mode of operation, whereby eachLED string (e.g., LED string 1322, 1380 and 1324) may be madeconcurrently conductive (e.g., by applying appropriate control signals1354, 1342 and 1356, respectively) such that current may be conducted byeach LED string (e.g., LED string 1322, 1380 and 1324) at the same timefor each time period 1502. As a result, the magnitude of currentconducted by each LED string (e.g., LED string 1322, 1380 and 1324) maybe reduced by the number of LED strings connected to node 1310 (e.g., 3)thereby increasing efficacy while maintaining the intensitysubstantially equal to the intensity obtained while operating in TDMAcurrent sharing mode.

In one embodiment, processor 1304 may be configured (e.g., via firmwareexecuting within processor 1304 or via wired network 1358 or wirelessnetwork 1360) to transition between TDMA current sharing mode and directdrive mode when the TDMA time slots (e.g., time slots 1504, 1506 and1508) are substantially equal to each other or within a percentage rangeof between zero percent and twenty percent (e.g., between about zeropercent and five percent) of each other. As per one example, if timeslots 1504 and 1506 constitute 35% of period 1502 and time slot 1508constitutes 30% of period 1502, processor 1304 may determine that timeslots 1504, 1506 and 1508 are substantially equal within a thresholdpercentage range of each other so as to justify a transition from TDMAcurrent sharing mode to direct drive mode in order to effectuatesubstantially the same intensity produced by each LED string but withsignificantly increased efficacy. In such an instance, for example, eachof LED strings 1322, 1380 and 1324 may be made concurrently conductive(e.g., via appropriate control signals 1354, 1342 and 1356,respectively) during each time period 1502. As a result, each of LEDstrings 1322, 1380 and 1324 may be concurrently conducting substantiallyless current (e.g., LED strings 1322, 1380 and 1324 may each presentsubstantially the same current load to node 1310 each conducting ⅓ theavailable current from DC stage 1340) as compared to a TDMA currentsharing mode thereby increasing efficacy while maintaining substantiallythe same intensity.

In alternate embodiments, as discussed in relation to FIG. 15D, a directdrive mode may be applied to less than all of the LED strings while theremaining LED strings may be operating in a TDMA current sharing mode.As per one example, LED strings 1322, 1380 and 1324 may be operating ina TDMA current sharing mode whereby time slots 1534 and 1536 may besubstantially equal (e.g., both time slots equal to 40% of period 1532)whereas time slot 1538 may be of a substantially less time duration(e.g., equal to 20% of period 1532). In such an instance, processor 1304may command both LED strings 1322 and 1380 to be concurrently conductiveduring time slots 1534 and 1536 to effectuate a direct drive mode viaappropriate control signals 1354 and 1342, respectively, such that bothLED strings 1322 and 1380 may be operating at substantially the sameintensity as compared to operation in a TDMA current sharing mode,except with half the magnitude of conducted current (e.g., LED strings1322 and 1380 may each present substantially the same current load tonode 1310 each conducting half the available current from DC stage 1340)and, therefore, substantially increasing efficacy for each LED of LEDstrings 1322 and 1380. LED string 1324, on the other hand, may continueto operate in a TDMA current sharing mode, whereby the full amount ofcurrent provided by DC stage 1340 may be exclusively conducted by LEDstring 1324 during time slot 1538.

In other embodiments as exemplified in FIG. 15E, power control signal1348 may be utilized by processor 1304 to further enhance efficacy byfirst decreasing a current magnitude output of DC stage 1340 and thentransferring operation to a direct drive mode to produce an equivalentintensity as compared to an average intensity that may be achieved usingTDMA current sharing mode. As per an example, LED strings 1322, 1380 and1324 may be operating in a TDMA current sharing mode at an intensityselected by processor 1304 as a percentage (e.g., 10%) of maximumintensity. In such an instance, processor 1304 may select 100% currentoutput from DC stage 1340 via control signal 1348 and subsequentlyselect each of LED strings 1322, 1380 and 1324 to be conductive duringtime slots 1544, 1546 and 1548, where each respective time slot may besubstantially equal to 10% of time period 1542 in order to achieve 10%intensity on average from each of LED strings 1322, 1380 and 1324.Alternately and in order to significantly increase efficacy, forexample, processor 1304 may instead select 30% current output from DCstage 1340 via control signal 1348 and subsequently select each LEDstring 1322, 1380 and 1324 to be concurrently conductive throughout timeperiod 1542 thereby allowing each respective LED string to conduct asubstantially decreased current magnitude (e.g., LED strings 1322, 1380and 1324 may each conduct ⅓ of the 30% current output from DC stage 1340to equal 1/10 the current magnitude as compared to the current magnitudeconducted in TDMA current sharing mode) except with substantiallyincreased efficacy and substantially the same intensity on average.

Turning to FIG. 15B, in any given TDMA period 1510, any one or more LEDstrings (e.g., any of LED strings 1322, 1380 and/or 1324 of FIG. 13) maybe denied a time slot (e.g., time slot 1514 does not provide for anactive current conduction state within which LED string 1380 may receivecurrent). As per an example, only two time slots (e.g., time slots 1512and 1516) may be allocated within which any two LED strings (e.g., LEDstrings 1322 and 1324, respectively) may receive any of an analog and/ora digitally controlled current signal.

In time slot 1512, for example, processor 1304 may command LED string1322 to conduct a percentage (e.g., 100%) of the maximum availablecurrent by causing a maximum magnitude of bias current from acorresponding DC stage (e.g., DC stage 1340) to be conducted by LEDstring 1322. In time slot 1516, LED string 1324 may similarly beprogrammed to receive an analog and/or digitally controlled currentsignal so that a percentage (e.g., 100%) of the maximum availablecurrent from DC stage 1340 may be received by LED string 1324.

It should be noted that since each of LED strings 1322 and 1324 receivea maximum bias current magnitude in each of respective time slots 1512and 1516 and since time slot 1512 is twice the duration of time slot1516, the average amount of current conducted by LED string 1322 overmultiple time periods 1510 is substantially equal to about ⅔ the maximumcurrent available from DC stage 1340 and the average amount of currentconducted by LED string 1324 over multiple time periods 1510 issubstantially equal to about ⅓ the maximum current available from DCstage 1340.

It should be further noted that current conducted by LED strings 1322and 1324 in each of time slots 1512 and 1516, respectively, may bemodulated (e.g., pulse width modulated) to further reduce the averageamount of current conducted over time. As discussed above, for example,any one of 256 duty cycle selections may be made by processor 1304 suchthat the amount of current conducted by each LED string 1322 and 1324 ineach time slot 1512 and 1516, respectively, may be further reduced onaverage by the duty cycle selection of control signals 1354 and 1356,respectively.

Turning to FIG. 15C, in any given TDMA period 1520, any one or more LEDstrings (e.g., any of LED strings 1322, 1380 and/or 1324 of FIG. 13) maybe denied a time slot (e.g., time slots 1524 and 1526 do not provide foran active current conduction state within which LED string 1380 and 1324may receive current). As per an example, only one time slot (e.g., timeslot 1522) may be allocated within which an LED string (e.g., LED string1322) may receive any of an analog and/or a digitally controlled currentsignal.

In time slot 1522, for example, processor 1304 may command LED string1322 to conduct a percentage (e.g., 100%) of the maximum availablecurrent by causing a maximum magnitude of bias current from acorresponding DC stage (e.g., DC stage 1340) to be conducted by LEDstring 1322. It should be noted that since LED string 1322 receives amaximum bias current magnitude in time slot 1522 and since time slot1522 is the same duration as time period 1520, the average amount ofcurrent conducted by LED string 1322 over multiple time periods 1520 issubstantially equal to all of the maximum current available from DCstage 1340.

It should be further noted that current conducted by LED string 1322 intime slot 1522 may be modulated (e.g., pulse width modulated) to furtherreduce the average amount of current conducted over time. As discussedabove, for example, any one of 256 duty cycle selections may be made byprocessor 1304 such that the amount of current conducted by LED string1322 in time slot 1522 may be further reduced on average by the dutycycle selection of control signal 1354.

As per an alternate example, DC stage 1340 may be commanded to a currentmagnitude of 1.2 A, but each of LED strings 1322, 1380 and 1324 may onlyrequire 0.4 A on average via appropriate PWM control of their associatedpower switches (e.g., FETs 1350, 1352 and 1386, respectively) to operateat their respective commanded intensity. In such an instance, 1.2 A maybe conducted instantaneously by any one LED string 1322, 1380 and 1324at a time (e.g., only one of LED strings 1322, 1380 and 1324 may beconductive at any given time), but through time division multiple access(TDMA) control, each LED string may be operating at 33% duty cycle toreceive only the required 0.4 A on average to operate at its commandedintensity. It should be noted that through analog and/or digital currentcontrol and proper time division multiple access to such controlledcurrent, any one LED string may operate at any intensity (e.g., 0-100%)at any given time (e.g., any one LED string may be conductive to themutual exclusion of all of the other LED string conductivity states) tooperate on average at the commanded intensity.

Turning to FIG. 16, indoor horticultural system 1600 is exemplified,which may include a horticultural lighting system (e.g., horticulturallighting fixtures 1604-1612 as exemplified by the lighting fixtures ofFIGS. 1, 9, 10, 11 and/or 13) each implementing any number of wiredcontrol topologies (e.g., DMX, I2C, Ethernet, USB, DALI, etc.) and/orany number of wireless control topologies (e.g., Wi-Fi, thread-basedmesh, Bluetooth, ZigBee, etc.) that may be utilized to control, forexample, intensity, color temperature and/or color spectrum as well asany other attribute of light that may be emitted by the horticulturallighting fixtures.

Indoor horticultural system 1600 may also contain any number of areasensors (e.g., sensors 1674-1677), which may be used to detect, forexample, occupancy, room temperature, humidity, etc. and may provide anassociated status signal (e.g., thread-based mesh network status signal)that may be indicative of the sensors' status (e.g., temperaturereading, humidity level, motion detection, etc.). Plant-based sensorsmay also be paired with each plant of the grow bed (e.g., plant/sensorpairs 1630/1631 through 1646/1647) so that parameters (e.g.,temperature, humidity, light intensity, color temperature, spectralcontent, moisture, pH, canopy height, etc.) may be sensed for eachplant, or group of plants, and reported at regular time intervals via anassociated status signal (e.g., thread-based mesh network statussignal). It should be noted that each sensor of FIG. 16 may include acomputing module (not shown), which may be used to administercommunications, conduct sensor measurements and sensormeasurement/status reporting and whose operational power may be derivedfrom a solar cell (not shown) and/or internal battery (not shown).

Indoor horticultural system 1600 may also include nutrient distribution1654 that may provide the nutrients and water that may be required byeach plant of each grow bed(s). Nutrient distribution may be implementedas a closed-loop system, whereby nutrients and water may be extractedfrom their respective storage containers (not shown) and mixed to properproportions. Once properly mixed, the nutrient solution may be pumped(e.g., at a monitored flow rate) into hydroponic flood benches and/ortrough benches (not shown) to be delivered for consumption by each plantof each grow bed that may be contained within indoor horticulturalsystem 1600. Any unused nutrient solution retrieved from nutrientdistribution 1654 may be collected, filtered and prepared to berecirculated to the hydroponic flood benches and/or trough benches.Nutrient distribution 1654 may also include sensors (not shown), whichmay be used to test the collected nutrient flow for any deficiencies andsubsequently reported as additional status information which may then beused to adjust (e.g., automatically via master controller 1688) thenutrient/water content for optimized growth of the associated plants inthe associated grow beds.

As shown, indoor horticultural system 1600 may include lighting systemsthat may be included within any facility that may exhibit structuralcomponents such as walls (not shown) and ceilings (e.g., ceiling 1696).Each of the lighting fixtures, sensors and associated control elementsof indoor horticultural system 1600, therefore, may be deployed withinsuch structural components of the facility as a fixed or permanentasset.

For example, light controller 1692 may be deployed within ceiling 1696as a fixed asset within indoor horticultural system 1600. Lightcontroller 1692 may, for example, include a DMX master controller (notshown) that may receive wireless commands (e.g., from master controller1688) and in response, may control the desired intensity of eachhorticultural light fixture 1604-1612 (e.g., each LED array of eachhorticultural light fixture 1604-1612) accordingly. In one embodiment,for example, each LED array of each horticultural light fixture1604-1612 may exist within the same DMX universe and may be responsiveto an 8-bit intensity control word received within its uniquelydesignated DMX slot from light controller 1692.

Other fixed assets within indoor horticultural system 1600 may include,for example, horticultural lighting fixtures 1604-1612 and theirassociated height control mechanisms (e.g., winch mechanisms that maycontrol the length of cable assemblies 1602). Cable assemblies 1602, forexample, may be controlled by a height controller (e.g., heightcontroller 1652) that may be used to raise and lower horticulturallighting fixtures 1604-1612 in accordance with the canopy height of theassociated plants (e.g., as may be reported by plant/sensor pairs1630/1631 to 1646/1647 to master controller 1688). For example, as theplants grow taller, it may be necessary to raise the associatedhorticultural lighting fixtures 1604-1612 in relation to the extendedheight of the associated plant canopies.

In one embodiment, each of the horticultural lighting fixtures andassociated sensors/controllers of indoor horticultural system 1600 maybe interconnected wirelessly (e.g., via a thread-based mesh network).Accordingly, for example, indoor horticultural system 1600 may beimplemented as a wireless personal area network (WPAN) utilizing aphysical radio layer (e.g., as defined by the IEEE 802.15.4communication standard). As such, the thread-based mesh network mayutilize an encapsulation and header compression mechanism (e.g.,6LoWPAN) so as to allow data packets (e.g., IPv6 data packets) to besent and received over the physical radio layer. Messaging between eachdevice within indoor horticultural system 1600 may be implemented usinga messaging protocol (e.g., user datagram protocol (UDP)), which may bepreferred over an alternative protocol such as the transmission controlprotocol (TCP).

In addition, each device may use an application layer protocol fordelivery of the UDP data packets to each device. Such application layerprotocols may include the Constrained Application Protocol (CoAP),Message Queue Telemetry Transport (MQTT) or the Extensible Messaging andPresence Protocol (XMPP) within the thread-based mesh network ascontrasted with the Hypertext Transport Protocol (HTTP) as may be used,for example, within Internet 1684. CoAP, for example, may be moreconducive for use by the thread-based mesh network, rather than HTTP,due to the smaller packet header size required by CoAP, which may thenyield smaller overall packet sizes required by the components of indoorhorticultural system 1600 interconnected by the thread-based meshnetwork.

In operation, some components (e.g., horticultural lighting fixtures1604-1612) interconnected by the thread-based mesh network of FIG. 16may be connected to an alternating current (AC) source that may be usedthroughout the facility for use with other components requiring AC powerfor operation, such as heating, ventilation and air conditioning (HVAC)systems, air circulators, humidifiers/dehumidifiers and CO₂ dispensingsystems 1694. Furthermore, operational power derived from the AC sourcemay be further controlled (e.g., via relays) so as to be compliant with,for example, the Energy Star® standard for energy efficiency aspromulgated jointly by the Environmental Protection Agency (EPA) and theDepartment of Energy (DOE).

In one embodiment, device 1686 may be used to manually operate indoorhorticultural system 1600 wirelessly (e.g., through the use of athread-based mesh network). For example, device 1686 may send a controlsignal to light controller 1692 via the thread-based mesh network tocause one or more horticultural lighting fixtures 1604-1612 toilluminate in accordance with a particular light prescription (e.g.,intensity, color temperature and/or color spectrum) as may be containedwithin database 1690. Alternately, device 1686 may send a control signalto height controller 1652 via the thread-based mesh network so as tocause the height between one or more horticultural lighting fixtures1604-1612 to change with respect to a height of the one or more plantcanopies contained within indoor horticultural system 1600. In alternateembodiments, master controller 1688 may completely automate theoperation of indoor horticultural system 1600 by accessing grow recipesfrom database 1690, which may then be used to control the lighting in aspecific manner to produce a specific effect (e.g., modify theintensity, color temperature and/or color spectrum of each ofhorticultural lights 1604-1612 to simulate a rising sun, a midday sunand a setting sun in direction 1698 from east to west).

Indoor horticultural system 1600 may, for example, be sensitive tocontrol signals as may be provided by controlling entities (e.g.,external BACnet network 1682) that may exist external to thethread-based mesh network of FIG. 16. As per an example, one or moreentities within indoor horticultural system 1600 may be BACnet enabled,which may allow communication with a BACnet enabled border router (e.g.,master controller 1688). In such an instance, control signals bound forindoor horticultural system 1600 may be transmitted by external BACnetnetwork 1682 via Internet 1684 and propagated throughout indoorhorticultural system 1600 via master controller 1688. Conversely, statusinformation related to indoor horticultural system 1600 may be gatheredby master controller 1688 and may then be disseminated to externalBACnet network 1682 via Internet 1684. Accordingly, many grow facilitiesas exemplified by FIG. 16 may exist and may be geographically dispersedand remotely controlled via external BACnet network 1682.

Each of horticultural light fixtures 1606-1612 may, for example,generate relatively wide beam patterns (e.g., beam patterns 1615-1621,respectively) that may be produced by a particular LED/lens combination(e.g., the LED/lens combination as discussed above in relation to FIG.6), which may produce maximum intensity at the edges of the beampattern. Accordingly, for example, the resulting light distribution(e.g., the light distribution of FIG. 7A) may produce a uniformilluminance onto a plant canopy directly below each of horticulturallight fixtures 1606-1612 (e.g., uniform illuminance distributions1622-1628) while producing relatively equal intensities on adjacentplants. In alternate embodiments, illuminance distributions 1622-1628may increase as the angle of incidence increases with respect to theoptical axis of illuminance distributions 1622-1628.

As an example, horticultural light 1606 may produce a uniformilluminance, or an increasing illuminance from centerbeam outward (e.g.,illuminance 1622) onto a plane that may be defined by the canopy ofplant 1632 due to the increasing intensity of light at increasing angleswith respect to the optical axis of horticultural light 1606. Since theintensity of light generated by horticultural light 1606 is greatest atthe edges of light distribution 1615, plants 1630 and 1634 may receive asubstantially equal intensity of light as received by plant 1632 fromhorticultural light 1606 owing to the effects of the inverse square lawas discussed above. In such an instance, each plant may not only receivea uniform illuminance, or an increasing illuminance from centerbeamoutward, onto its canopy by an associated horticultural light fixture,but may also receive substantially equal intensities of light on thesides of the plant by adjacent horticultural light fixtures, therebymore correctly simulating sunlight, since light is being received byeach plant from multiple angles. It should be noted that horticulturallight fixtures 1604-1612 may be arranged not only as a linear-array, butas a two-dimensional array (e.g., arranged along rows and columns) suchthat each plant may receive light from its associated horticulturallight fixture and adjacent horticultural light fixtures at all anglesformed from a 360-degree light distribution (e.g., each plant mayreceive a substantially uniform cone of light from its associated andadjacent horticultural light fixtures).

Plants on the edge of each grow bed (e.g., plants 1630 and 1646) mayreceive light from their associated horticultural lighting fixturesconfigured at angles that are different than the angles of horticulturallighting fixtures 1606-1612. For example, horticultural lightingfixtures 1604 and 1605 may be angled (e.g., via height controller 1652and associated cable assemblies 1602) as shown to direct light ontotheir associated plants (e.g., plants 1630 and 1646, respectively) aswell as the adjacent plants (e.g., plants 1632 and 1644, respectively).In addition, each of horticultural light fixtures 1604-1605 may, forexample, generate relatively narrow beam patterns (e.g., beam patterns1613-1614, respectively) that may be produced by a particular LED/lenscombination (e.g., the LED/lens combination as discussed above inrelation to FIG. 3), which may similarly produce maximum intensity atthe edges of the beam pattern as discussed above in relation to FIGS. 4Aand 4B so as to illuminate adjacent plants (e.g., 1632 and 1644,respectively) with substantially the same intensity as associated plants1630 and 1632, respectively.

In alternate embodiments, each of horticultural light fixtures 1604-1612may, for example, generate relatively wide beam patterns (e.g., beampatterns 1613-1621, respectively) that may be produced by bare LEDs(e.g., standard LED packages producing a Lambertian beam pattern withoutan associated lens) where each bare LED may be mounted at varying angleswith respect to one another. In such an instance, for example, a firstbare LED may be mounted within a light fixture (e.g., light fixture1606) such that the optical axis of the first LED may align with a lightdistribution (e.g., light distribution 1622) that may be directed towarda target (e.g., plant 1632). Second and third bare LEDs may alternatelybe mounted within a light fixture (e.g., light fixture 1606) at opposingangles such that the optical axes of the first and second bare LEDs mayalign with the edges of a light distribution (e.g., light distribution1615). For example, a second bare LED may be mounted within lightfixture 1606 such that its optical axis may be directed at itsrespective target (e.g., plant 1630) and a third bare LED may be mountedwithin light fixture 1606 such that its optical axis may be directed atits respective target (e.g., plant 1634). Accordingly, light fixture1606 may, for example, not only provide direct lighting to plant 1632,but may also provide cross-lighting for adjacent plants 1630 and 1634without the use of lenses that may optically vary the light distributedby light fixture 1606.

Turning to FIG. 17, a schematic diagram of a lighting system isexemplified, whereby the forward voltage of one or more LEDs of an LEDstring (e.g., LED string 1732) of a light fixture (e.g., master lightfixture 1722) may be utilized as a relatively low-current power supplyfor auxiliary purposes (e.g., to provide a 0-10V dimming controllerwithout the need for a dedicated 0-10V controller power supply). Forexample, the forward voltage of several LEDs (e.g., two LEDs 1702) maycombine in series to form a cumulative forward voltage equal to the sumof the individual forward voltage of each LED (e.g., 2*6=12 volts atnode 1734) and may be used as an auxiliary supply voltage. The impedanceof a rheostat (e.g., potentiometer 1704) may be selected such that verylittle current may be derived from the LED string at node 1734 whileallowing a variable voltage to be selected manually (e.g., by anoperator in control of potentiometer 1704) and applied to thenon-inverting input of operational amplifier 1710. In one embodiment,switch 1708 may be implemented as a removable, hard-wired selector(e.g., PCB jumper) that may allow the wiper voltage of potentiometer1704 to be applied to operational amplifier 1710.

In operation, operational amplifier 1710 may seek to maintain thevoltage at its inverting input substantially equal to the voltage at itsnon-inverting input through operation of negative feedback applied toits inverting input as shown. As such, the conductive state oftransistor 1728 may be selected by operational amplifier 1710 (e.g.,through selection of the voltage, V_(b), applied to the base terminal oftransistor 1728) such that the voltage at node 1726 (e.g., a 0-10Vcontrol voltage, V_(CTRL)) may be maintained to be proportional to thevoltage selected by potentiometer 1704 (V_(POT)) according to voltagefollower equation (1):

$\begin{matrix}{{V_{CTRL} = {V_{POT}( {1 + \frac{R_{1720}}{R_{1712}}} )}},} & (1)\end{matrix}$

where R₁₇₂₀ is the resistance magnitude of resistor 1720 and R₁₇₁₂ isthe resistance magnitude of resistor 1712. Writing V_(CTRL) in terms ofthe current (I₁₇₂₈) conducted by transistor 1728:

V _(CTRL) =V _(b) +I ₁₇₂₈ R ₁₇₁₄ +V _(EB),  (2)

where R₁₇₁₄ is the resistance magnitude of resistor 1714 and V_(EB) isthe emitter-base voltage of transistor 1728 and combining equation (1)with equation (2):

$\begin{matrix}{{I_{1728} = \frac{{V_{POT}( {1 + \frac{R_{1720}}{R_{1712}}} )} - V_{b} - V_{EB}}{R_{1714}}},} & (3)\end{matrix}$

it can be seen from equation (3) that the magnitude of current conductedby transistor 1728, I₁₇₂₈, may be directly dependent upon the basevoltage, V_(b), of transistor 1728 as applied by operational amplifier1710. Turning back to equation (1), the voltage at node 1726 (V_(CTRL))follows the voltage selected by potentiometer 1704 (V_(POT)) as modifiedby the gain constant (1+R₁₇₂₀/R₁₇₁₂) and the current conducted bycurrent sink 1718 may be adjusted (e.g., increased) by adjusting (e.g.,decreasing) the base voltage, V_(b), of transistor 1728 via operationalamplifier 1710. As the voltage at node 1726, V_(CTRL), decreases below athreshold voltage magnitude, shunt transistor 1736 may be utilized toshunt the voltage at node 1726, V_(CTRL), to a reference voltage (e.g.,the collector-emitter voltage of transistor 1736 referenced to groundpotential) so as to extend the voltage control range at node 1726 belowthat which may be accommodated by transistor 1728.

Master light fixture 1722 (e.g., via 0-10V driver 1730) and slave lightfixtures 1724 may be configured with 0-10V drivers that may sourcecurrent into node 1726 and may derive their intensity control signal,V_(CTRL), from node 1726 as well. As the number of slave light fixtures1724 increases, so may the current magnitude conducted by current sink1718. Through operation of equation (3) as discussed above, it can beseen that an increase in current conducted by current sink 1718 (e.g.,as may be required through the addition of slave light fixtures 1724 andmaster light fixture 1722) may be accommodated by a correspondingdecrease in base voltage, V_(b). Accordingly, the number of slave lightfixtures and master light fixture that may be accommodated by currentsink 1718 may be directly proportional to the current conductioncapability of current sink 1718. In one embodiment, for example, thecurrent conduction capability of current sink 1718 may be selected to beapproximately 50 mA, which may then accommodate up to 99 slave lightfixtures (and one master light fixture 1722), such that up to 100, 0-10Vdrivers may each source 500 uA of current into node 1726.

In an alternate embodiment, switch 1708 (e.g., a PCB jumper) may beselected such that a wireless control module (e.g., wireless control1706) may instead control the voltage at the non-inverting input ofoperational amplifier 1710, which may then control the voltage at node1726, V_(CTRL), as discussed above. It can be seen, therefore, that theintensity of multiple lights within an indoor horticultural system(e.g., horticultural lights 1604-1612 of indoor horticultural system1600 of FIG. 16) may be controlled by a light controller (e.g., lightcontroller 1692 of FIG. 16) operated either through manual control(e.g., potentiometer 1704) or through wireless control (e.g., wirelesscontrol 1706) such that all horticultural lights 1604-1612 may beoperated at substantially equal intensities via a single control input.

Turning to FIG. 18, an alternate embodiment of agricultural lightfixture 1800 is exemplified whereby arrays of LEDs may not be arrangedin columns or rows, but may instead be arranged in clusters of betweenabout 2-10 LEDs per cluster (e.g., groups of 3-4 LEDs in each cluster1802 and 1812). Each cluster of agricultural light fixture 1800 may, forexample, include any combination of color spectrum LEDs and/or colortemperature LEDs. Further, each individual LED in each cluster ofagricultural light fixture 1800 may exist within its own LED string, orconversely, may share an LED string with one or more other LEDs in thesame cluster.

As per one example, a cluster (e.g., cluster 1812) may be comprised offour LEDs (e.g., LEDs 1804, 1806, 1808 and 1810), whereby LED 1804 mayexist within a first LED string (e.g., LED string 1322 of FIG. 13), LED1806 may exist in a second LED string (e.g., LED string 1380 of FIG. 13)and LEDs 1808-1810 may exist in a third LED string (e.g., LED string1324 of FIG. 13). The remaining clusters of agricultural light fixture1800 may be similarly configured, whereby for example, one such cluster1802 may include LED 1814 that may exist within the same LED string asLED 1804, LED 1816 that may exist within the same LED string as LED 1806and LEDs 1818-1820 that may exist within the same LED string as LEDs1808-1810.

LED 1804 may, for example, be implemented with an LED having a specificcolor spectrum (e.g., blue) or a specific color temperature (e.g.,6500K), LED 1806 may, for example, be implemented with an LED having aspecific color temperature (e.g., 3000K white LED) and LEDs 1808-1810may, for example, be implemented with LEDs having a specific colorspectrum (e.g. red). As discussed above, the remaining clusters withinagricultural light fixture 1800 may be similarly configured, whereby forexample, LED 1814 may, for example, be implemented with an LED havingthe same specific color spectrum or the same specific color temperatureas LED 1804, LED 1816 may, for example, be implemented with an LEDhaving the same specific color temperature as LED 1806 and LEDs1818-1820 may, for example, be implemented with LEDs having the samespecific color spectrum as LEDs 1808-1810.

In one embodiment, the number of LEDs that may exist within any givenLED string may be chosen such that the combined forward voltage of anyone LED string is substantially equal to the combined forward voltage ofthe remaining LED strings. As per one example, LEDs 1804, 1814 and theremaining LEDs in similar positions within the remaining clusters ofagricultural light fixture 1800 (e.g., the upper left-hand corner ofeach cluster) may exist within the same LED string (e.g., LED string1322 of FIG. 13) where the LED string may exhibit a combined forwardvoltage equal to the product of the number of LEDs in the LED string(e.g., 45 clusters with one LED per cluster equals 45 LEDs) and theforward voltage of each LED (e.g., 3 volts) for a combined forwardvoltage approximately equal to 45*3=135 volts.

As per another example, LEDs 1808-1810 and the remaining LEDs in similarpositions within the remaining clusters of agricultural light fixture1800 (e.g., the lower row of each cluster) may exist within the same LEDstring (e.g., LED string 1324 of FIG. 13) where the LED string mayexhibit a combined forward voltage equal to the product of the number ofLEDs in the LED string. However, since the forward voltage of each LEDin LED string 1324 may be different (e.g., 2 volts) than the forwardvoltage of LEDs in the other LED strings, an increased number (e.g.,67-68 LEDs) for a combined forward voltage approximately equal to67*2=134 volts or 68*2=136 volts may be utilized. In addition, since ahigher number of clusters (e.g., 45) exist than are needed toaccommodate two LEDs per cluster, some of the clusters may include onlya single, 2-volt LED. In such an instance, those clusters exhibitingonly a single, 2-volt LED may be symmetrically arranged within the arrayof clusters of agricultural light fixture 1800 (e.g., every othercluster may exhibit a single, 2-volt LED).

As discussed in more detail below, each cluster of agricultural lightfixture 1800 may include an optical puck (e.g., optical puck 1950 asexemplified in the top orthographic view of FIG. 19B and the bottomorthographic view of FIG. 19C) that may provide an optical lens for eachLED in each cluster having between about 2-10 LEDs per cluster (e.g., 4optical lenses 1952 per cluster as exemplified in FIG. 19B). Eachoptical lens 1952 of optical puck 1950 may, for example, provide opticalcharacteristics (e.g., optical characteristics as discussed above inrelation to FIGS. 3-4 and/or 6-7), but may be arranged differently(e.g., as compared to the lens arrays as discussed above in relation toFIGS. 2A and 2B). Instead, the LED/lens pairs of agricultural lightfixture 1800 may be arranged in groups of about 2-10 LED/lens pairs(e.g., 4 LED/lens pairs), each LED of which may be in electricalcommunication with one or more LEDs of the remaining LED/lens pairs asdiscussed above.

As discussed in more detail below, cover 1822 may be disposed inrelation to agricultural light fixture 1800 such that each optical puckmay protrude through apertures disposed within cover 1822 (e.g.,aperture 1824), such that no further optical treatment (e.g., sheetlens) may be applied to the light generated from each cluster beyond theoptical treatment provided by each lens of each optical puck.Accordingly, increased efficiency (e.g., between about 6-12% increasedefficiency) may be achieved by eliminating the use of a sheet lens.

Turning to FIG. 19A, orthographic view 1900 of a portion of agriculturallight fixture 1800 of FIG. 18 is illustrated, with the cover (e.g.,cover 1822 of FIG. 18) removed to expose the inner rib architecture. Inparticular, multiple ribs (e.g., ribs 1904 and 1916-1922) may extendapproximately the length of agricultural light fixture 1800 and maysupport multiple PCBs (e.g., PCBs 1902 and 1908-1914) that may bedisposed upon ribs 1904 and 1916-1922, respectively, and may also extendapproximately the length of agricultural light fixture 1800. Asillustrated, each rib (e.g., rib 1904) may, for example, support a PCB(e.g., PCB 1902) that may include multiple optical pucks (e.g., opticalpucks 1906), each optical puck including multiple (e.g., 3-4) lenses.Clusters of LEDs (not shown) may be disposed below each optical puck(e.g., LEDs may be disposed within indented portions 1954 of opticalpuck 1950 as exemplified in FIG. 19C), such that each lens of eachoptical puck may be disposed in relation to each corresponding LED ofeach cluster. As per one example, each LED and corresponding lens ofeach LED/lens pair may be disposed in relation to one another asdiscussed above (e.g., as exemplified in relation to LED 306/lens 314 ofFIG. 3 and LED 606/lens 614 of FIG. 6).

PCB 1902 may include electrically conductive traces (not shown), suchthat each LED of each cluster may be electrically connected to eachcorresponding LED of each remaining cluster on PCB 1902. Furthermore,corresponding LEDs of the remaining clusters of the remaining PCBs(e.g., PCBs 1908-1914) may be electrically interconnected to formmultiple LED strings (e.g., LED strings 1322, 1380 and 1324 as discussedabove in relation to FIG. 13), whereby each LED string may exhibit acombined forward voltage that may be substantially equal as discussedabove. Each LED string may then be illuminated on command as discussedabove (e.g., as in relation to FIGS. 13 and 15).

Heat generated by illumination of the LEDs of the clusters ofagricultural light fixture 1800 mounted to each of PCBs 1902 and1908-1914 may be conducted away from PCBs 1902 and 1908-1914 by thecorresponding ribs 1904 and 1916-1922, respectively. Accordingly, panel1924 may receive the heat conducted by each of ribs 1904 and 1916-1922by virtue of the conductive path implemented by each rib to panel 1924.Additionally, an electrically insulative, thermally conductive layer(e.g., a polyester film not shown) may exist to conduct heat to panel1822). The conducted heat may then be removed from agricultural lightfixture 1800 by convection through circulation of air past panel 1924and cover 1822. In addition, ribs 1904 and 1916-1922 may provideconsiderable structural support within agricultural light fixture 1800,such that in operation (e.g., agricultural light fixture 1800 isinverted as compared to the position shown), panel 1924 may provide astorage surface, or shelf, upon which utility articles may be storedwhile agricultural light fixture 1800 operates within its associatedagricultural facility.

Each optical puck may include a trough (e.g., trough 1926 of FIG. 19B),within which a compressible device (e.g., an O-ring not shown) may beinstalled, such that once the panel (e.g., panel 1822 of FIG. 18)encloses agricultural light fixture 1800, panel 1822 may engage eachO-ring of each optical puck to seal the interior of agricultural lightfixture 1800 from contaminants (e.g., water, rain, dust, oil, etc.). Inaddition, gasket 1928 may be utilized to compress against panel 1822 tofurther protect agricultural light fixture 1900 from externalcontaminants (e.g., in accordance with the InternationalElectrotechnical Commission Ingress Protection 66 (IP66) standard ofprotection).

Turning to FIG. 20, alternate embodiments of lighting fixtures areexemplified, in which bare LEDs (e.g., LEDs without optically varyinglenses) may be positioned to project a substantially even targetilluminance across a flat surface, or conversely, to project anilluminance onto a flat surface that increases as the angle increasesbetween the lighting fixture and the flat surface. In particular, LEDsexhibiting varying beam angles, but without optical lenses, may beutilized within agricultural lighting fixtures 2002 and 2022, wherebyLED arrays (e.g., LED arrays 2006, 2010, 2014) may exist withinagricultural lighting fixture 2002 (e.g., on panels 2004, 2008 and 2012,respectively) and LED arrays (e.g., LED arrays 2026, 2030 and 2034) mayexist within agricultural lighting fixture 2022 (e.g., on panels 2024,2028 and 2032, respectively) to project illumination beam widths 2016,2018, 2020 from agricultural lighting fixture 2002 and to projectillumination beam widths 2036, 2038 and 2040 from agricultural lightingfixture 2022.

As exemplified in FIG. 20, the illumination projected by LED arrays 2010and 2030 may exhibit wider beam patterns (e.g., greater than 120 degreeFWHM) as compared to the narrower beam patterns (e.g., less than 90degree FWHM) projected by LED arrays 2006, 2014, 2026 and 2034.Accordingly, the beam patterns projected by LED arrays 2006 and 2014 mayoverlap with the beam pattern projected by LED array 2010 at overlapportions 2052 and 2054, respectively. Similarly, the beam patternsprojected by LED arrays 2026 and 2034 may overlap with the beam patternprojected by LED array 2030 at overlap portions 2056 and 2058,respectively.

In addition, the area of overlap portions 2052 and 2054 on surface 2050may be increased or decreased depending upon the angle at which LEDarrays 2006 and 2014 are projecting light with respect to LED array2010. Similarly, the area of overlap portions 2056 and 2058 on surface2050 may be increased or decreased depending upon the angle at which LEDarrays 2026 and 2034 are projecting light with respect to LED array2030.

It can be seen, for example, that by decreasing angles 2042 and 2044,the area of overlap portions 2052 and 2054 increases. Similarly, forexample, by decreasing angles 2046 and 2048, the area of overlapportions 2056 and 2058 increases. Accordingly, the amount ofcross-lighting produced by the agricultural lighting fixtures of FIG. 20may be increased or decreased, which may in turn increase or decreasethe illuminance projected onto surface 2050. As such, illuminancevariations may be effected without the use of optically varying lenses.

Turning to FIG. 21, cooling aspects of agricultural light fixture 2100(e.g., light fixture 100 of FIG. 1) are exemplified. Fan 2108 may, forexample, draw external air 2102 into an interior of agricultural lightfixture 2100 and may further cause the drawn air to travel in direction2104 within agricultural light fixture 2100. As the drawn air travelswithin agricultural light fixture 2100, heat may be extracted fromwithin agricultural light fixture 2100 by convection and expelled viaexhaust port 2110 as expelled air flow 2106. Accordingly, expelled airflow 2106 may be expelled from within agricultural light fixture 2100 ina direction opposite to the optical axis of agricultural light fixture2100 (e.g., optical axis 2112).

It can be seen, therefore, that if agricultural light fixture 2100 wereapplied to an indoor horticultural system (e.g., as lights 1604-1612 ofindoor horticultural system 1600 of FIG. 16), expelled air may bedirected toward ceiling 1696 away from plants 1630-1646. By directingthe expelled air away from plants 1630-1646, any excess heat that mayaffect leaf temperature and potentially the reduction of transpirationof the leaves closest to agricultural light fixture 2100 may bemitigated.

Turning to FIG. 22, cooling aspects of agricultural light fixture 2200(e.g., light fixture 900 of FIG. 9) are exemplified. Fan 2212 may, forexample, draw external air 2202 into an interior of agricultural lightfixture 2200 and may further cause the drawn air to travel in directions2204 and 2206 within agricultural light fixture 2200. As the drawn airtravels within agricultural light fixture 2200, heat may be extractedfrom within agricultural light fixture 2200 by convection and expelledvia exhaust ports 2214 and 2216 as expelled air flows 2210 and 2208,respectively. Accordingly, expelled air flows 2210 and 2208 may beexpelled from within agricultural light fixture 2200 in a directionopposite to the optical axis of agricultural light fixture 2200 (e.g.,optical axis 2218).

It can be seen, therefore, that if agricultural light fixture 2200 wereapplied to an indoor horticultural system (e.g., as lights 1604-1612 ofindoor horticultural system 1600 of FIG. 16), expelled air may bedirected toward ceiling 1696 away from plants 1630-1646. By directingthe expelled air away from plants 1630-1646, any excess heat that mayaffect leaf temperature and potentially the reduction of transpirationof the leaves closest to agricultural light fixture 2200 may bemitigated.

Other aspects and embodiments of the present invention will be apparentto those skilled in the art from consideration of the specification andpractice of the invention disclosed herein. It is intended, therefore,that the specification and illustrated embodiments be considered asexamples only, with a true scope and spirit of the invention beingindicated by the following claims.

1. A light fixture, comprising: a plurality of LED channels coupled to acurrent node and configured to receive a current signal from the currentnode, wherein one of the plurality of LED channels includes a firstportion of LEDs having a first forward voltage and a second portion ofLEDs having a second forward voltage, the first forward voltage beinggreater than the second forward voltage; a one or more shunt devicesdisposed in relation to one or more of the first portion of LEDs; and aprocessor coupled to each of the one or more shunt devices andconfigured to vary the current signal conducted by the first portion ofLEDs by controlling a conductivity state of each of the one or moreshunt devices.
 2. The light fixture of claim 1, wherein the firstportion of LEDs include white LEDs.
 3. The light fixture of claim 1,wherein the second portion of LEDs include red LEDs.
 4. The lightfixture of claim 1, wherein the one or more of the shunt devices arecoupled in parallel with a single LED of the first portion of LEDs. 5.The light fixture of claim 1, wherein the one or more of the shuntdevices are coupled in parallel with multiple LEDs of the first portionof LEDs.
 6. The light fixture of claim 1, wherein the processor controlsthe conductivity state of each shunt device using a PWM signal.
 7. Thelight fixture of claim 1, wherein the one or more shunt devices areconfigured as voltage controlled variable resistors.
 8. The lightfixture of claim 7, wherein the processor further controls a voltagedrop across the one or more shunt devices.
 9. A method of controlling acumulative forward voltage of an LED string, comprising: arranging afirst portion of LEDs in series within the LED string, the first portionof LEDs having a first forward voltage; interspersing a second portionof LEDs in series among the first portion of LEDs, the second portion ofLEDs having a second forward voltage that is greater than the firstforward voltage; disposing a shunt device across one or more of thesecond portion of LEDs; and configuring the shunt device to produce avariable voltage across the one or more of the second portion of LEDs.10. The method of claim 9, wherein a color of light produced by thefirst portion of LEDs is different than a color of light produced by thesecond portion of LEDs.
 11. The method of claim 10, wherein the variablevoltage changes the cumulative forward voltage of the LED string.
 12. Amethod of controlling light emitted by an LED string, comprising:arranging a first portion of LEDs in series within the LED string;interspersing a second portion of LEDs in series among the first portionof LEDs; disposing a shunt device across one or more of the secondportion of LEDs; conducting a current signal through the LED string; andconfiguring the shunt device to conduct at least a portion of thecurrent signal away from the one or more of the second portion of LEDs.13. The method of claim 12, wherein the shunt device is configured toreduce an intensity of light generated by the one or more of the secondportion of LEDs.
 14. The method of claim 12, wherein the shunt device isconfigured to eliminate an intensity of light generated by the one ormore of the second portion of LEDs.